Refactor test/e2e/testdata to use go template based replacements

[swghosh]

For extensible replacement of field values in the yaml(s) used within e2e testdata/ through config structs,
the go text/template allows for better replacement support; aids readability as well.

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[swghosh]

/test e2e-operator

[swghosh]

/test e2e-operator

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[lunarwhite]

@swghosh Thanks for this enhancement!

Assuming you have already examined this patch locally to see if the replacements work as expected, I don’t foresee anything preventing us from merging this PR.

/label qe-approved
/lgtm

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This pull-request has been approved by: lunarwhite, swghosh

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