🔥 Add support for application/problem+json

[rhburt]

Description

I have added support for RFC7807 application/problem+json alongside the existing implementation for application/json. According to the RFC, there are no mandatory fields for problem+json that distinguish it from regular json content; so, I have only added the ProblemJson methods that send requests/responses and associated tests that require the mime type.

This is my first PR to this project so please let me know if I need to change anything. Thanks.

EDIT:
I have changed the ProblemJSON methods to CustomJSON methods that take in the Content-Type header as a parameter. This allows us to support all JSON mime type extensions, such as "application/problem+json".

Fixes #2701

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• For new functionalities I follow the inspiration of the express js framework and built them similar in usage
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation - /docs/ directory for https://docs.gofiber.io/
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• If new dependencies exist, I have checked that they are really necessary and agreed with the maintainers/community (we want to have as few dependencies as possible)
• I tried to make my code as fast as possible with as few allocations as possible
• For new code I have written benchmarks so that they can be analyzed and improved

Commit formatting:

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[welcome]

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[ReneWerner87]

thx for the effort
lets discuss some small points

[rhburt]

Benchmarks without variadic ctype parameter:

go test -run=^$ -bench=Benchmark_Ctx_CustomJSON_Ctype -benchmem -count=4

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2
cpu: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
Benchmark_Ctx_CustomJSON_Ctype-12        4666432               276.2 ns/op            56 B/op          2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4483280               262.5 ns/op            56 B/op          2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4582852               258.5 ns/op            56 B/op          2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4697461               263.6 ns/op            56 B/op          2 allocs/op
PASS
ok      github.com/gofiber/fiber/v2     5.957s

Benchmarks with variadic ctype parameter:

go test -run=^$ -bench=Benchmark_Ctx_CustomJSON_Ctype -benchmem -count=4

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2
cpu: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
Benchmark_Ctx_CustomJSON_Ctype-12        4613229               269.6 ns/op            56 B/op         2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4484907               256.6 ns/op            56 B/op         2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4681248               244.3 ns/op            56 B/op         2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4635668               229.8 ns/op            56 B/op         2 allocs/op
PASS
ok      github.com/gofiber/fiber/v2     5.673s

go test -run=^$ -bench=Benchmark_Ctx_CustomJSON_No_Ctype -benchmem -count=4

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2
cpu: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
Benchmark_Ctx_CustomJSON_No_Ctype-12             4810928               264.0 ns/op          56 B/op           2 allocs/op
Benchmark_Ctx_CustomJSON_No_Ctype-12             4475920               243.4 ns/op          56 B/op           2 allocs/op
Benchmark_Ctx_CustomJSON_No_Ctype-12             4942119               251.4 ns/op          56 B/op           2 allocs/op
Benchmark_Ctx_CustomJSON_No_Ctype-12             4984884               250.4 ns/op          56 B/op           2 allocs/op
PASS
ok      github.com/gofiber/fiber/v2     5.877s

[ReneWerner87]

Benchmarks without variadic ctype parameter:

go test -run=^$ -bench=Benchmark_Ctx_CustomJSON_Ctype -benchmem -count=4

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2
cpu: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
Benchmark_Ctx_CustomJSON_Ctype-12        4666432               276.2 ns/op            56 B/op          2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4483280               262.5 ns/op            56 B/op          2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4582852               258.5 ns/op            56 B/op          2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4697461               263.6 ns/op            56 B/op          2 allocs/op
PASS
ok      github.com/gofiber/fiber/v2     5.957s

Benchmarks with variadic ctype parameter:

go test -run=^$ -bench=Benchmark_Ctx_CustomJSON_Ctype -benchmem -count=4

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2
cpu: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
Benchmark_Ctx_CustomJSON_Ctype-12        4613229               269.6 ns/op            56 B/op         2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4484907               256.6 ns/op            56 B/op         2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4681248               244.3 ns/op            56 B/op         2 allocs/op
Benchmark_Ctx_CustomJSON_Ctype-12        4635668               229.8 ns/op            56 B/op         2 allocs/op
PASS
ok      github.com/gofiber/fiber/v2     5.673s

go test -run=^$ -bench=Benchmark_Ctx_CustomJSON_No_Ctype -benchmem -count=4

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2
cpu: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
Benchmark_Ctx_CustomJSON_No_Ctype-12             4810928               264.0 ns/op          56 B/op           2 allocs/op
Benchmark_Ctx_CustomJSON_No_Ctype-12             4475920               243.4 ns/op          56 B/op           2 allocs/op
Benchmark_Ctx_CustomJSON_No_Ctype-12             4942119               251.4 ns/op          56 B/op           2 allocs/op
Benchmark_Ctx_CustomJSON_No_Ctype-12             4984884               250.4 ns/op          56 B/op           2 allocs/op
PASS
ok      github.com/gofiber/fiber/v2     5.877s

ok then add this feature to the JSON function

[efectn]

Lgtm

[ReneWerner87]

@rhburt pls solve the last part

[rhburt]

Apologies for the delay @ReneWerner87, it should pass the linting checks now.

[welcome]

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