docs: expand CONTRIBUTING with component workflows, testing, and OWNERS routing

[isumitsolanki]

What type of PR is this?

/kind documentation

What this PR does / why we need it:

CONTRIBUTING.md is expanded so contributors can see how this monorepo is organized, what to run before sending a PR (unit tests, make verify, shell checks, when E2E/kOps applies), and how review routing works via OWNERS for the main components (cloud-controller-manager, auth-provider-gcp, gke-gcloud-auth-plugin, cluster assets, providers, and tests).

Which issue(s) this PR fixes:

Fixes #1005

Special notes for your reviewer:

NONE

Does this PR introduce a user-facing change?

No. This only updates contributor-facing documentation.

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @isumitsolanki. Thanks for your PR.

I'm waiting for a kubernetes 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.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: isumitsolanki
Once this PR has been reviewed and has the lgtm label, please assign hdp617 for approval. For more information see the Code Review Process.

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Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
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[zhang-xuebin]

/assign @hdp617