fix(webhook): do not require rsa_public_key field in credentials secrets when working with jwt HMAC algorigthms

[pmalek]

What this PR does / why we need it:

Do not requiere the rsa_public_key field in credential secrets when working with jwt HMAC credentials.

The algorithm values are compares against https://docs.konghq.com/hub/kong-inc/jwt-signer/configuration/#config-enable_hs_signatures

Which issue this PR fixes:

Fixes #5736

Related: #5159

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.7%. Comparing base (8c49b29) to head (b195a9c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5737     +/-   ##
=======================================
- Coverage   71.7%   71.7%   -0.1%     
=======================================
  Files        175     175             
  Lines      18141   18147      +6     
=======================================
- Hits       13019   13014      -5     
- Misses      4170    4185     +15     
+ Partials     952     948      -4     

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[team-k8s-bot]

The backport to release/3.1.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/3.1.x release/3.1.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.1.x
# Create a new branch
git switch --create backport-5737-to-release/3.1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 c9978fabd5f82275db1cd0135608d8b7d7351891
# Push it to GitHub
git push --set-upstream origin backport-5737-to-release/3.1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.1.x

Then, create a pull request where the base branch is release/3.1.x and the compare/head branch is backport-5737-to-release/3.1.x.