Unify the way to process errors for xPolicy

[shawnh2]

Description:

nowadays, the BTP and SP use different strategy dealing with errors, the BTP directly return the error from translate methods, but SP joins the errors then return. maybe it's better to unify the way to process all the translated errors.

[optional Relevant Links:]

originally post in #2848 (comment)

[shawnh2]

recommended way:

• join the errors together then return, this will allow users to quickly get a overall translation errors look, like it's been done in SecurityPolicy:
  

  gateway/internal/gatewayapi/securitypolicy.go

  Line 299 in 01a123a

  err, errs error

• give a hint about which part of the spec got translation error, like it's been done in BackbendTrafficPolicy:
  

  gateway/internal/gatewayapi/backendtrafficpolicy.go

  Line 329 in 01a123a

  return errors.Wrap(err, "RateLimit")

[shawnh2]

assign myself, since it's related to #2631

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 30 days.