Fix bug: Move the CUSTOM_TLS_CERT from subscriber config to subscribe…

[RipulHandoo]

…r secret

Proposed changes

It Move the CUSTOM_TLS_CERT from subscriber config to subscriber secret.
fixes #3943

Types of changes

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• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices applies)

Checklist

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• I have read the CONTRIBUTING doc
• I have signed the commit for DCO to be passed.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

Dependency

• Please add the links to the dependent PR need to be merged before this (if any).

Special notes for your reviewer:

[RipulHandoo]

Hey @namkyu1999 , could you review this and help identify why the checks aren't passing?

[namkyu1999]

Hey @RipulHandoo , You don't have to care about backend-unit-tests check. It's not your problem

[vanshBhatia-A4k9]

I think these changes will be required for both the ns scope and cluster scope infra manifests right?
As well as appropriate changes in the subscriber where the env variables' values are being set. cc: @Saranya-jena

[Saranya-jena]

@RipulHandoo have you tested the changes?

[Jonsy13]

Looks good, please make same changes under namespace directory as well.