feat: Cache glab env config to improve overall command performance

[pgollangi]

Cache glab env config which avoids loading env file from file system which in turn improves overall command performance

Description
Have a map of env config on first load which will used for all subsequent environment searches.

Related Issue
Closes #144

Motivation and Context

How Has This Been Tested?
Benchmarks without cache (bench-before.txt):

BenchmarkGetEnv-4   	   50974	     23479 ns/op	     816 B/op	       6 allocs/op
BenchmarkGetEnv-4   	   51392	     23192 ns/op	     816 B/op	       6 allocs/op
BenchmarkGetEnv-4   	   51847	     24126 ns/op	     816 B/op	       6 allocs/op
BenchmarkGetEnv-4   	   51861	     23541 ns/op	     816 B/op	       6 allocs/op
BenchmarkGetEnv-4   	   51854	     23891 ns/op	     816 B/op	       6 allocs/op

Benchmarks with cache (bench-after.txt):

BenchmarkGetEnv-4   	92289234	        12.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkGetEnv-4   	100000000	        12.2 ns/op	       0 B/op	       0 allocs/op
BenchmarkGetEnv-4   	85945108	        12.7 ns/op	       0 B/op	       0 allocs/op
BenchmarkGetEnv-4   	92740719	        12.3 ns/op	       0 B/op	       0 allocs/op
BenchmarkGetEnv-4   	92294202	        12.5 ns/op	       0 B/op	       0 allocs/op

Overall improvement is almost 100%:

$ benchstat bench-before.txt bench-after.txt
name      old time/op    new time/op    delta
GetEnv-4    23.6µs ± 2%     0.0µs ± 2%   -99.95%  (p=0.008 n=5+5)

name      old alloc/op   new alloc/op   delta
GetEnv-4      816B ± 0%        0B       -100.00%  (p=0.008 n=5+5)

name      old allocs/op  new allocs/op  delta
GetEnv-4      6.00 ± 0%      0.00       -100.00%  (p=0.008 n=5+5)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[pull-assistant]

Best reviewed: commit by commit

---

Optimal code review plan

     feat: Cache glab env config to improve overall command performance

Powered by Pull Assistant. Last update 7f1ccaf ... 7f1ccaf. Read the comment docs.

[profclems]

goos: linux
goarch: amd64
pkg: glab/internal/config
BenchmarkGetEnv-4       83589975                14.0 ns/op
BenchmarkGetEnv-4       83691345                14.7 ns/op
BenchmarkGetEnv-4       85224246                14.0 ns/op
BenchmarkGetEnv-4       84176131                14.0 ns/op
BenchmarkGetEnv-4       78762896                16.2 ns/op

This is a great performance improvement. It is very negligible

[profclems]

@all-contributors please add @pgollangi for maintenance

[allcontributors]

@profclems

I've put up a pull request to add @pgollangi! 🎉