Fix km-tab label regression introduced by #8049

[KhizerRehan]

What this PR does / why we need it:
This PR fixes the regression introduced by #8049 that broke the Clusters Overview page by causing the label-template content query to capture unrelated TemplateRef instances produced by structural directives inside the tab body (e.g. *matHeaderCellDef from mat-table).

Why It Broke

@ContentChild(TemplateRef) matches the first TemplateRef instance in projected content. Angular structural directives such as *matHeaderCellDef, *matCellDef, *matRowDef, *ngIf, etc. desugar to and produce TemplateRef instances.

Which issue(s) this PR fixes:

Fixes #

What type of PR is this?
/kind bug
/kind regression

Special notes for your reviewer:

Does this PR introduce a user-facing change? Then add your Release Note here:

NONE

Documentation:

NONE

Test issue:

NONE

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[KhizerRehan]

I could have reverted #8049 PR but IMO, directive approach is still better as it would help incase Angular migrations run. There won't be issue due to duplicate names.