feat(log): enhance memory efficiency for the zap logger with fields

[tessig]

An often used pattern for the flamingo.Logger is to store an instance with prepared fields in a struct field.
The logger is then initialized with the fields in the struct's Inject method.

The underlying zap logger is then cloned and in big project we allocate a lot of memory for this.

This change keeps the fields in the layer of the flamingo logger until it comes to a message write. Then the fields are passed to zap.

The benchmark in core/zap/logger_test.go promises better memory efficiency with this change.

[tessig]

In addition, let's also consider the upcoming structured logger in Go https://go.googlesource.com/proposal/+/master/design/56345-structured-logging.md

[tessig]

benchstat for this change (core/zap/logger_test.go)

goos: darwin
goarch: arm64
pkg: flamingo.me/flamingo/v3/core/zap
                               │  old.bench  │              new.bench              │
                               │   sec/op    │   sec/op     vs base                │
Logger/withField-1-log-10        3.354µ ± 0%   1.642µ ± 1%  -51.05% (n=50)
Logger/withFields-1-log-10       1.629µ ± 1%   1.312µ ± 1%  -19.46% (n=50)
Logger/withField-each-log-10     8.399µ ± 0%   6.760µ ± 1%  -19.52% (n=50)
Logger/withFields-many-logs-10   9.830µ ± 1%   9.402µ ± 0%   -4.35% (p=0.000 n=50)
geomean                          4.608µ        3.420µ       -25.78%

                               │   old.bench   │          new.bench           │
                               │     B/op      │     B/op      vs base        │
Logger/withField-1-log-10         9.009Ki ± 0%   2.813Ki ± 0%  -68.77% (n=50)
Logger/withFields-1-log-10        2.769Ki ± 0%   1.579Ki ± 0%  -42.96% (n=50)
Logger/withField-each-log-10     12.769Ki ± 0%   6.567Ki ± 0%  -48.57% (n=50)
Logger/withFields-many-logs-10    9.533Ki ± 0%   8.334Ki ± 0%  -12.58% (n=50)
geomean                           7.423Ki        3.949Ki       -46.80%

                               │ old.bench  │         new.bench          │
                               │ allocs/op  │ allocs/op   vs base        │
Logger/withField-1-log-10        64.00 ± 0%   28.00 ± 0%  -56.25% (n=50)
Logger/withFields-1-log-10       26.00 ± 0%   20.00 ± 0%  -23.08% (n=50)
Logger/withField-each-log-10     144.0 ± 0%   108.0 ± 0%  -25.00% (n=50)
Logger/withFields-many-logs-10   170.0 ± 0%   164.0 ± 0%   -3.53% (n=50)
geomean                          79.89        56.12       -29.75%

[github-actions]

Package	Line Rate	Health
flamingo.me/flamingo/v3/core/auth	13%	❌
flamingo.me/flamingo/v3/core/auth/fake	50%	➖
flamingo.me/flamingo/v3/core/auth/http	40%	❌
flamingo.me/flamingo/v3/core/auth/oauth	49%	❌
flamingo.me/flamingo/v3/core/cache	54%	➖
flamingo.me/flamingo/v3/core/gotemplate	87%	✔
flamingo.me/flamingo/v3/core/healthcheck/interfaces/controllers	76%	✔
flamingo.me/flamingo/v3/core/healthcheck	66%	➖
flamingo.me/flamingo/v3/core/internalauth/application	100%	✔
flamingo.me/flamingo/v3/core/internalauth	100%	✔
flamingo.me/flamingo/v3/core/locale/application	87%	✔
flamingo.me/flamingo/v3/core/locale/domain	75%	✔
flamingo.me/flamingo/v3/core/locale/interfaces/controllers	100%	✔
flamingo.me/flamingo/v3/core/locale/interfaces/templatefunctions	92%	✔
flamingo.me/flamingo/v3/core/locale	59%	➖
flamingo.me/flamingo/v3/core/oauth/application	4%	❌
flamingo.me/flamingo/v3/core/oauth/domain	62%	➖
flamingo.me/flamingo/v3/core/oauth	55%	➖
flamingo.me/flamingo/v3/core/requestlogger	100%	✔
flamingo.me/flamingo/v3/core/requesttask	10%	❌
flamingo.me/flamingo/v3/core/robotstxt	50%	➖
flamingo.me/flamingo/v3/core/runtime	77%	✔
flamingo.me/flamingo/v3/core/security/application/role	95%	✔
flamingo.me/flamingo/v3/core/security/application	98%	✔
flamingo.me/flamingo/v3/core/security/application/voter	100%	✔
flamingo.me/flamingo/v3/core/security/interface/controller	100%	✔
flamingo.me/flamingo/v3/core/security/interface/middleware	72%	➖
flamingo.me/flamingo/v3/core/security	59%	➖
flamingo.me/flamingo/v3/core/zap	43%	❌
flamingo.me/flamingo/v3/framework/cmd	12%	❌
flamingo.me/flamingo/v3/framework/config	49%	❌
flamingo.me/flamingo/v3/framework/flamingo	40%	❌
flamingo.me/flamingo/v3/framework	29%	❌
flamingo.me/flamingo/v3/framework/opencensus	88%	✔
flamingo.me/flamingo/v3/framework/prefixrouter	43%	❌
flamingo.me/flamingo/v3/framework/systemendpoint	27%	❌
flamingo.me/flamingo/v3/framework/testutil	0%	❌
flamingo.me/flamingo/v3/framework/web	49%	❌
Summary	49% (3339 / 6746)	❌