feat(meta): watch and reload license key from file

[BugenZhao]

Signed-off-by: Bugen Zhao [email protected]I hereby agree to the terms of the RisingWave Labs, Inc. Contributor License Agreement.

What's changed and what's your intention?

Add a CLI argument of --license-key-file for the meta node, which enables a background task to watch and reload license key from that file, simplifying license key rotation in Cloud.

Some notes:

• Only take effect on the meta node, as the license key will still be propagated through system parameters to all other nodes.
• Can also be configured with env var RW_LICENSE_KEY_PATH.
• Manually specifying the license key via system parameters (license_key), initial configuration (system.license_key), or the RW_LICENSE_KEY environment variable is still possible but not recommended when using --license-key-file, as it can easily get overwritten if the key file's content changes will be rejected when --license-key-file is specified. (see refactor(meta): reject directly setting license key when it's managed by watching a file #18823)

Added a unit test.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Documentation

• My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)

Release note

See description above.

[fuyufjh]

LGTM

[fuyufjh]

Manually specifying the license key via system parameters (license_key), initial configuration (system.license_key), or the RW_LICENSE_KEY environment variable is still possible but not recommended when using --license-key-file, as it can easily get overwritten if the key file's content changes.

How about adding an error message for ALTER SYSTEM SET license_key TO '...' to notify users they are using it incorrectly?

[BugenZhao]

How about adding an error message for ALTER SYSTEM SET license_key TO '...' to notify users they are using it incorrectly?

Oops. Missed this. Will refine in the following PR.

[arkbriar]

typo found 🤣

[arkbriar]

Discussed with @BugenZhao elsewhere, here's the conclusion: RW_LICENSE_KEY_PATH will be kept instead of being changed to the RW_LICENSE_KEY_FILE in the PR description.