Compress Harbormaster build logs inline

Summary:
Ref T5822.

• After a log is closed, compress it if possible.
• Provide bin/harbormaster archive-logs to make it easier to change the storage format of logs.

Test Plan:

• Ran bin/harbormaster archive-logs on a bunch of logs, compressing and decompressing them without issues (same hashes, same decompressed size across multiple iterations).
• Ran new builds, verified logs were compressed after they closed.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T5822

Differential Revision: https://secure.phabricator.com/D15380