docs: add rfc for move i18n logic to frontend

[kakcy]

This pull request proposes moving the i18n (internationalization) logic entirely to the frontend to simplify the backend code. The changes include adding detailed documentation and examples of the new error handling design using GRPC's ErrorInfo and removing the existing LocalizedMessage code from the backend.

#1253

[cre8ivejp]

It would be better to put this log logic into a common function.
Depending on the function, we handle many errors, making the function too long.
One of the reasons for moving the localizer to the front end is also to improve code readability.

WDYT?

Suggested change

	dt, err := statusEmailIsEmpty.WithDetails(
	&errdetails.ErrorInfo{
	Reason: "INVALID",
	Domain: "account.bucketeer.io",
	Metadata: map[string]string{
	"messageKey": "account.invalid.empty",
	"feild": "email",
	},
	})
	if err != nil {
	return statusInternal.Err()
	}
	return dt.Err()
	return error.NewError(...)

[kakcy]

Thank you, Good idea!

It's certainly more readable that way, so I do that when coding.

[Ubisoft-potato]

Basically, we will use canary release to switch i18n logic from backend to fronted, right?

[kakcy]

Yes, that's right. Bucketeer essentially uses a canary release.

[hvn2k1]

I was wondering if we can add multiple error metadata, e.g.

[]map[string]string{
  {
    "messageKey": "account.invalid.empty",
    "field":      "email",
  },
  {
    "messageKey": "account.invalid.empty",
    "field":      "phone_number",
  },
}

[kakcy]

Although it is stated in the RFC, it uses GRPC's ErrorInfo, so the type of Metadata cannot be changed.
If multiple errors are returned, we plan to return multiple ErrorInfo's.

		dt, err := statusEmailIsEmpty.WithDetails(
			&errdetails.LocalizedMessage{
				Locale:  localizer.GetLocale(),
				Message: localizer.MustLocalizeWithTemplate(locale.InvalidArgumentError, "email"),
			},
			&errdetails.ErrorInfo{
				Reason: "INVALID",
				Domain: "account.bucketeer.io",
				Metadata: map[string]string{
					"messageKey": "account.invalid.empty",
					"feild":      "email",
				},
			},
			&errdetails.ErrorInfo{
				Reason: "INVALID",
				Domain: "account.bucketeer.io",
				Metadata: map[string]string{
					"messageKey": "account.invalid.empty",
					"feild":      "phone_number",
				},
			})