wip: Serverless GCP docs foundation

[apiarian-datadog]

What does this PR do? What is the motivation?

This PR coordinates our work to refresh our Serverless GCP documentation. It is a long-lived branch that we will merge into master once all the changes are ready. Please open PRs off of and into branch for this project.

Merge instructions

Please do not merge this branch for now.

Merge readiness:

• [ ] Ready for merge

For Datadog employees: Merge queue is enabled in this repo. Your branch name MUST follow the <name>/<description> convention and include the forward slash (/). Without this format, your pull request will not pass in CI, the GitLab pipeline will not run, and you won't get a branch preview. Getting a branch preview makes it easier for us to check any issues with your PR, such as broken links.

If your branch doesn't follow this format, rename it or create a new branch and PR.

To have your PR automatically merged after it receives the required reviews, add the following PR comment:

/merge

Additional notes

[github-actions[bot]]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/aleksandr.pasechnik/serverless-gcp-docs-refresh/serverless/google_cloud/
• https://docs-staging.datadoghq.com/aleksandr.pasechnik/serverless-gcp-docs-refresh/serverless/google_cloud/google_cloud_run
• https://docs-staging.datadoghq.com/aleksandr.pasechnik/serverless-gcp-docs-refresh/serverless/google_cloud/google_cloud_run_functions
• https://docs-staging.datadoghq.com/aleksandr.pasechnik/serverless-gcp-docs-refresh/serverless/google_cloud/google_cloud_run_functions_1st_gen
• https://docs-staging.datadoghq.com/aleksandr.pasechnik/serverless-gcp-docs-refresh/serverless/google_cloud/google_cloud_run_in_process

[iadjivon]

Created a Jira Card for review: DOCS-11015

[github-actions[bot]]

ℹ️ Documentation Team Review

No documentation team review is required for this pull request.