fix(plugins): ai proxy cloud identity transformers

[tysoekong]

Summary

• Fixed a bug where cloud identity authentication was not used in ai-request-transformer and ai-response-transformer plugins.
• Re-factor "cloud SDK auth" function to be shared across many AI plugins.

Checklist

• The Pull Request has tests - already has them
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - already are docs

Issue reference

AG-94

[tysoekong]

@fffonion @liverpool8056 I done all the comments. I think many is just that I haven't commented it so well.

[gszr]

@tysoekong It looks like this PR includes parts of https://github.com/Kong/kong-ee/pull/9930/files plus other changes. Could you rework commits in such a way that it closely matches https://github.com/Kong/kong-ee/pull/9930/files (including changelog) and any addition is in its own separate commit? As it's right now, we would have to squash and merge, which would result in unrelated commits being squashed together

[tysoekong]

@gszr Again this one is deliberate! It is because there are EE-only features in this plugin, that are only adjusted in https://github.com/Kong/kong-ee/pull/9930/files

It's all in the plan.

I will rebase ee 9930 when this gets picked.

[gszr]

@gszr Again this one is deliberate! It is because there are EE-only features in this plugin, that are only adjusted in Kong/kong-ee#9930 (files)

It's all in the plan.

I will rebase ee 9930 when this gets picked.

@tysoekong please squash last commit onto the one above it so we can rebase and merge.

[gszr]

some minor comments; otherwise LGTM!

[oowl]

LGTM

[team-gateway-bot]

Cherry-pick failed for master, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally.

git remote add upstream https://github.com/kong/kong-ee
git fetch upstream master
git worktree add -d .worktree/cherry-pick-13487-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13487-to-master-to-upstream
git checkout -b cherry-pick-13487-to-master-to-upstream
ancref=$(git merge-base 64a0dd1c5c22f8be266742247f6e30aabd6c08ee ce673be082229d185cd12e727160f131653a6115)
git cherry-pick -x $ancref..ce673be082229d185cd12e727160f131653a6115