helm: Allow the use of existing policy configMap

[agmimidi]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Enables the use of an existing policy configMap. This can be useful in complex scenarios where the policy file needs to be constructed via other means (e.g. An existing gitOps/IaC setup)

Which issue(s) this PR fixes:
NONE

Special notes for your reviewer:
Default behaviour is kept as-is, change only takes effect when existingPolicyConfigMap is set to true.

Does this PR introduce a user-facing change?
See above

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:
This PR also modifies the README file

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: agmimidi / name: Angelos Mimidis (5905d09, e30c73c, 9462c34, d2bfafe)
• ✅ login: a7i / name: Amir Alavi (afa64e5, 715ad74)

[k8s-ci-robot]

Welcome @agmimidi!

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[k8s-ci-robot]

Hi @agmimidi. Thanks for your PR.

I'm waiting for a kubernetes-sigs 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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[damemi]

/ok-to-test

[agmimidi]

/retest-required

[a7i]

/lgtm

[a7i]

/retitle helm: Allow the use of existing policy configMap
/lgtm

Thank you for your contribution @agmimidi

[a7i]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: a7i

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