Closes #133.

This needs to temporarily update all of our workflows and Docker image builds to ensure that they can reach the cometbft-db repository. I've logged an issue to keep track of reverting this in #158.

I'm currently manually running our nightly E2E tests on this branch to ensure that this still works: https://github.com/cometbft/cometbft/actions/runs/3952269253

This will have to be manually backported to v0.37.x and v0.34.x.

After this change, while the repos are still private, to be able to build the Docker images and run the E2E tests locally you'll need to do the following for each shell in which you're working:

export GOPRIVATE=github.com/cometbft
# This is needed because we need to grant access to the private cometbft-db repo 
# _within_ the Docker container build operation. Note the space before the "export"
# command - this prevents your shell from storing this in the history.
 export GO_MODULES_TOKEN="... a GitHub API token here..."

Your GitHub API token must have full access (read/write) to all repositories (i.e. the repo checkbox when configuring permissions). See https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token

I'd recommend setting an expiry of 30 days to any tokens used for this purpose, so we don't accidentally leave them lingering.

PR checklist

• Tests written/updated, or no tests needed
• CHANGELOG_PENDING.md updated, or no changelog entry needed
• Updated relevant documentation (docs/) and code comments, or no
  documentation updates needed