fix(plugins): add realm to removed fields

[nowNick]

Summary

Basic-auth and key-auth added new field "realm" but it was not added to "removed_fields" which breaks backwards compat between new CPs and old DPs. Adding realm to removed fields fixes the issue.

Checklist

• The Pull Request has tests
• 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 - PUT DOCS PR HERE

Issue reference

KAG-4516

[team-gateway-bot]

Backport failed for release/3.6.x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin release/3.6.x
git worktree add -d .worktree/backport-13042-to-release/3.6.x origin/release/3.6.x
cd .worktree/backport-13042-to-release/3.6.x
git switch --create backport-13042-to-release/3.6.x
git cherry-pick -x 420b3b6ceb17d84fb84486e0de72635fb4408c45

[team-gateway-bot]

Successfully created backport PR for release/3.7.x:

• [backport -> release/3.7.x] fix(plugins): add realm to removed fields #13127

[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-13042-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13042-to-master-to-upstream
git checkout -b cherry-pick-13042-to-master-to-upstream
ancref=$(git merge-base a11338a8f1ac7f869967fc74660380f11b051bb0 00abf103c277a3c74985b40db6647c615fb9efe6)
git cherry-pick -x $ancref..00abf103c277a3c74985b40db6647c615fb9efe6

[kikito]

@nowNick I am not sure we need to backport this to 3.6 in CE

[nowNick]

@kikito I think we do. However the backport needs to be tweaked a little because it'll only need basic-auth changes (the other - key-auth was changed in 3.7).