Gcp key detector

[LucasAndradeDias]

• Please check if the PR fulfills these requirements

• [X] Tests for the changes have been added

• [X] Docs have been added / updated

• [ ] All CI checks are green

• What kind of change does this PR introduce? This changes adds to detect-secrets a new plugin to find Google Cloud API keys and oauth2 client ids.

• What is the current behavior? When detect secrets finds a GCP API key in code, it shows the key as 64base key and as GCP Keys. With oauth2 cgp client-id the detect-secrets does not find it as secrets.

• What is the new behavior (if this is a feature change)? With the currently changes, the detect secrets is now able to correctly show infos about GCP Keys.

• Does this PR introduce a breaking change? No changes are need.

• Other information: Hi, I'am Lucas and I working on a team where we are interested on using Detect-secrets in our CI pipeline. Although this projects is already completed and it has much plugins, we miss some of detections like GCP, Firebase and Facebook tokens plugins. And that's the reason I'am making this pull request, to help detect-secrets to help us and the community in general.

[jpdakran]

Hi. Please merge master to your branch to re-run CI.

[chrislin22]

I have seen this PR stale for over a year - can we try it again? Thanks. @LucasAndradeDias @jpdakran

[lorenzodb1]

@chrislin22 if you need these changes, feel free to open a PR yourself with what's in here so we can review and merge that instead