Improve documentation on E2E tests

[salasberryfin]

/kind documentation

Describe the solution you'd like
While working on #1053, I've encountered a few obstacles to run E2E tests locally and I haven't found the documentation to be very detailed on how E2E tests are actually structured and how to use them as a developer. Thanks to @richardcase, I've been able to identify a few things missing from my configuration but I think it would be great, especially for new or relatively new contributors, to have a nuanced, easy to follow documentation on how CAPG E2E tests are structured and how a user can leverage them to improve their development experience.

Anything else you would like to add:

This is the E2E section from the CAPZ book which can be used as a reference.

[professorabhay]

Hey @salasberryfin, Can I do this?

[salasberryfin]

Hey @professorabhay, thanks for volunteering to work on this. It would be better to have confirmation from any of the cluster-api-gcp-maintainers @richardcase @cpanato @dims.

[salasberryfin]

/assign

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[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues.

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