[docseng-37] copy sourced integrations earlier in the build process to generate placeholder pages

[bgdeutsch]

What does this PR do? What is the motivation?

This aims to solve the missing placeholder pages from integrations problem.

• separates placeholders from the make dependencies chain so it can happen further down the line. we don't generate placeholders locally, so there's no need to call on it in the Makefile.
• update make update_websites_sources_module to use hugo mod vendor, copy the sourced integrations markdown files from websites-sources into docs, and remove the vendor directory immediately. this should only happen in the CI. the _vendor folder is already gitignored and there is logic to prevent it from running locally anyway, so it would never be committed.

new order of operations would be:

• dependencies
• update_websites_sources_module
• placeholders
  ...
• build_site

now we have the integrations in the file system, we can generate placeholders for them.

https://datadoghq.atlassian.net/browse/DOCSENG-37

Merge instructions

Merge readiness:

• Ready for merge

For Datadog employees:

Your branch name MUST follow the <name>/<description> convention and include the forward slash (/). Without this format, your pull request will not pass 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.

[6/5/2025] Merge queue has been disabled on the documentation repo. If you have write access to the repo, the PR has been reviewed by a Documentation team member, and all of the required checks have passed, you can use the Squash and Merge button to merge the PR. If you don't have write access, or you need help, reach out in the #documentation channel in Slack.

Additional notes

QA integrations page: https://docs-staging.datadoghq.com/brian.deutsch/docseng-37-placehold-apw-integrations/integrations/
QA integration details pages
pages that don't have placeholders in live have them in this preview for every language. for example:

• https://docs-staging.datadoghq.com/brian.deutsch/docseng-37-placehold-apw-integrations/es/integrations/google-cloud-platform
• https://docs-staging.datadoghq.com/brian.deutsch/docseng-37-placehold-apw-integrations/ko/integrations/celery/

[github-actions]

✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!