Use feature flag to create internal LB for self hosted templates

[nawazkh]

What type of PR is this?
/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Part of #5296

Special notes for your reviewer:

• This PR follows Create and add InternalILB as a CAPZ feature flag #5304

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• cherry-pick candidate

Release note:

Create ILB when feature flag: APIServerILB is enabled

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