feat(plugins): enable ai plugins to read request body from buffered file

[fffonion]

Summary

• feat(plugins): enable ai plugins to read request body from buffered file
• feat(pdk): add argument to allow request body read from disk

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

AG-39

#13211

[liverpool8056]

Do we need update removed_fields correspondingly?

[fffonion]

@liverpool8056 yes, i didn't notice removed_fields is also present on CE, will fix.

[fffonion]

I did a force push to port the backward compat tests from EE PR.

[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-13158-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13158-to-master-to-upstream
git checkout -b cherry-pick-13158-to-master-to-upstream
ancref=$(git merge-base 4664b907c86cf95d8ad98c7f51dce768c52070c3 eba070f49480b40d6c3449a80aeea8e3c88cc64b)
git cherry-pick -x $ancref..eba070f49480b40d6c3449a80aeea8e3c88cc64b

[locao]

@fffonion could you take care of the manual cherry-pick, please?

[dol]

IMHO it's safer to read the file content as binary. local file, err = io.open(body_file, "rb"). Just to be safe. https://www.lua.org/pil/21.2.2.html