Make log rotation configurable

[lava]

📔 Description

This PR adds minimal configurability to the rotating file sink used for spdlog.

It adds the option vast.log-rotation to turn off rotation, which is required for production use where VAST's log rotation may interfere with log rotation configured in external programs like systemd or logrotated.

The size threshold, number of rotated log files, and whether to use time-based logrotate are not made configurable, since we did not have anyone asking for these features yet.

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

[dominiklohmann]

The option should probably be named vast.disable-log-rotation with the default being false so it's in line with the other boolean options.

[dominiklohmann]

Ran this locally and it works as expected. Just had some nits. Please implement before merging.