[WIP] Add ipv6 support to CAPG

[sayantani11]

What type of PR is this?

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):
Fixes #478

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

ipv6 support

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: sayantani11
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[k8s-ci-robot]

@sayantani11: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-gcp-build	814c559	link	true	/test pull-cluster-api-provider-gcp-build
pull-cluster-api-provider-gcp-test	814c559	link	true	/test pull-cluster-api-provider-gcp-test
pull-cluster-api-provider-gcp-make	814c559	link	true	/test pull-cluster-api-provider-gcp-make
pull-cluster-api-provider-gcp-e2e-test	814c559	link	true	/test pull-cluster-api-provider-gcp-e2e-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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