ci: testing with cel policies

[JaydipGabani]

What this PR does / why we need it:

• Modifies the testing workflow to run gator verify with cel and rego engines
• Tests cel and rego policies with gatekeeper
• Adds cel source for requiredLables and allow-priviledge-escalation

Which issue(s) does this PR fix (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged): Fixes #

Special notes for your reviewer:

[JaydipGabani]

@maxsmythe I added CEL source from your draft PR #503 here as well, that leaves you with 3 other policies to write CEL source for.

[maxsmythe]

Can you drop the CEL from my draft PR? I'd rather only have one SOT for that, and just rebase/merge once the build system is ready, otherwise feedback will get clobbered.

[ritazh]

Can you drop the CEL from my draft PR? I'd rather only have one SOT for that, and just rebase/merge once the build system is ready, otherwise feedback will get clobbered.

Per this https://github.com/open-policy-agent/gatekeeper-library/pull/519#discussion_r1594796796 all updates for "Allow Privilege Escalation" policy have been removed

[ritazh]

@JaydipGabani ptal conflicts