[release] v1.28.0 - Transport override option & bug fixes (#221)

### New Features
  - Option to override the internal HTTP client's transport.
  ### Improvements
  - Better type conversion, now supports golang 
"enums"
  ### Fixes
- User persistent store evaluation schema for `explicit_parameters`
fixed to be consistent with other SDKs






>Included In This Release
>- 8f92476 kenny-statsig
>   - Add Transport Option to allow egress proxies (#217)
>- 3ad0fae kenny-statsig
>   - Fix lint errors (#218)
>- a85cc88 kenny-statsig
>   - Fix GCIR test (#220)
>- 3c50265 kenny-statsig
>   - Fix type conversion for custom type definitions (#204)
>- 9f37bc1 kenny-statsig
>   - Fix type of explicit parameters (#219)

statsig_metadata.go

@@ -14,7 +14,7 @@ type statsigMetadata struct {
 func getStatsigMetadata() statsigMetadata {
 	return statsigMetadata{
 		SDKType:         "go-sdk",
-		SDKVersion:      "v1.27.1",
+		SDKVersion:      "v1.28.0",
 		LanguageVersion: runtime.Version()[2:],
 		SessionID:       SessionID(),
 	}