Jetpack CLI: check and update monorepo docker image automatically once a day

[kraftbj]

Proposed changes:

• Add automatic daily check for updated automattic/jetpack-monorepo:latest Docker image
• Support FORCE_PULL=1 environment variable to force an immediate image update check
• Cache the last check timestamp in tools/docker/data/.monorepo-image-check to avoid checking more than once per 24 hours

Other information:

• Have you written new tests for your changes, if applicable? (N/A - shell script change)
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)? (N/A)

Jetpack product discussion

N/A - Internal tooling improvement

Does this pull request change what data or activity we track or use?

No

Testing instructions:

Test automatic daily check:

1. Delete the cache file if it exists: rm tools/docker/data/.monorepo-image-check
2. Run any jp command: jp --help
3. Verify you see "Checking for latest monorepo image..." and it runs docker pull
4. Run jp --help again immediately
5. Verify it does NOT check for the image again (no pull message)
6. Check the cache file was created: ls -la tools/docker/data/.monorepo-image-check

Test FORCE_PULL environment variable:

1. Run: FORCE_PULL=1 jp install
2. Verify you see "Forcing image update due to FORCE_PULL environment variable..." and it checks for updates
3. Verify the command still executes properly after the check

Test 24-hour expiry:

1. Create an old cache file: touch -t 202501010000 tools/docker/data/.monorepo-image-check
2. Run: jp --version
3. Verify it checks for the latest image again (cache is > 24 hours old)

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[kraftbj]

Thanks for the review @anomiex!

✅ Updated all 6 instances to use [[ ]] instead of [ ] for bash conditionals.

Regarding $EPOCHSECONDS: I tested and found that while it works in modern bash (5.3+), it returns an empty string in macOS's default bash 3.2.57. Since this script uses #!/usr/bin/env bash which will use the system bash on macOS, I kept $(date +%s) for bash 3.2 compatibility.

Note: I know I just said this, but I'm letting the AI tooling still post this as part of testing these tools.

[anomiex]

Seems reasonable, seems to work. One optional suggestion inline, feel free to ignore.

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[anomiex]

LGTM. Might want to update the PR description to remove reference to the --latest-image flag, to avoid potential confusion later.