✨ Add PriorityQueue feature flag

[nikParasyr]

What this PR does / why we need it:
Add support for controller-runtime PriorityQueue.
To do this:

• introduce feature flags on the provider
• create new feature flag that when set enables the controller-runtime PriorityQueue
• document feature flags and how to enable them
• document the PriorityQueue feature flag with upstream links

Which issue(s) this PR fixes:
Fixes #2820

Special notes for your reviewer:

1. Opted to add this behind a feature flag. Reasoning is:
   a. keeping it similar with other providers
   b. makes it easier to remove at a later stage as based on upstream priorityQueue will become default
2. Feature flag implementation is heavily based on the implementation of cluster-api
3. I'm struggling a bit to see how i can unit test this, i have run titl environments to see if the feature flag mechanism works and it does

TODOs:

• squashed commits
• if necessary:
  • includes documentation
  • adds unit tests

/hold

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[k8s-ci-robot]

Hi @nikParasyr. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[nikParasyr]

Some notes about this:

• This will work fine when capo is installed through clusterctl (as they use envsub) but if someone uses the release manifests to directly install from it wont work for them
• I opted for EXP_CAPO_PRIORITY_QUEUE to differentiate from capi EXP_PRIORITY_QUEUE, not sure if this is needed

[lentzi90]

/ok-to-test

[bnallapeta]

/lgtm

[lentzi90]

Code looks good. A couple of comments on the docs.

[lentzi90]

Thank you for this!
/approve
/hold cancel

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bnallapeta, lentzi90

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• OWNERS [lentzi90]

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[nikParasyr]

I think this misses the /lgtm label
( was removed with my push )

[lentzi90]

Yes, lgtm is always removed when there are changes.
@bnallapeta could you please re-lgtm if the docs changes look ok to you?

[bnallapeta]

/lgtm