test: add unit test for flag trigger

[kakcy]

Fixes #684

This pull request primarily includes adding unit tests for FlagTrigger and changes to the Bucketeer project's "pkg/feature/api" package. This change focuses on refactoring the FeatureService structure and related methods in api.go and flag_trigger.go to use the new v2fs package for feature storage. Additionally, error handling has been simplified for several methods, and the "generateTriggerURL" method no longer returns an error.

Here are the most important changes:

Add unit test for flag trigger.

Refactoring to use v2fs package:

• pkg/feature/api/api.go: Imported the v2fs package and its FeatureStorage and FlagTriggerStorage types. These were then added as fields to the FeatureService struct, replacing direct usage of the mysqlClient. The NewFeatureService function was also updated to initialize these new fields. [1] [2] [3]
• pkg/feature/api/api_test.go: Similar changes were made in the test file, where mock instances of FeatureStorage and FlagTriggerStorage are now created and used in the createFeatureService and createFeatureServiceNew functions. [1] [2] [3]

Simplification of error handling:

• pkg/feature/api/flag_trigger.go: In several methods, the error handling for generateTriggerURL has been removed, as this function no longer returns errors. Instead, the URL is directly assigned to triggerURL. Additionally, error handling in ResetFlagTrigger and DeleteFlagTrigger has been simplified to return a single error status. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Refactoring of FeatureService methods:

• pkg/feature/api/flag_trigger.go: All methods in this file that previously created new instances of FlagTriggerStorage or FeatureStorage now use the instances stored in the FeatureService struct. This includes the GetFlagTrigger, FlagTriggerWebhook, and generateTriggerURL methods. [1] [2] [3]

[kentakozuka]

Thanks!
left some suggestions :)

[kentakozuka]

Suggested change

	if err != nil {
	t.Errorf("generateTriggerURL() [full] error = %v", err)
	}

[kentakozuka]

Suggested change

	if err != nil {
	t.Errorf("generateTriggerURL() [masked] error = %v", err)
	}

[kentakozuka]

Suggested change

	ctx := createContextWithToken()
	ctx = metadata.NewIncomingContext(ctx, metadata.MD{
	"accept-language": []string{"ja"},
	})
	ctx = metadata.NewIncomingContext(
	createContextWithToken(),
	metadata.MD{"accept-language": []string{"ja"}},
	)

[kakcy]

@kentakozuka
Thank you for your suggestions!
I adopted it because it was necessary.
dbad210
f80df54

[kentakozuka]

LGTM 👍

[kakcy]

Thank you for the reviews!