Preserve timestamps in build directory

[leedxw]

I would like to deploy static assets with consistent Last-Modified: headers (and indeed Etag: which is derived from the filesize and timestamp in nginx). Partly for performance, partly for archive information.

Therefore I would like a deploy switch for timestamps that

• does full history clones
• Uses git-restore-mtime on every checkout

(This may require apt install git-restore-mtime or dnf install git-tools as part of setup.)

This would provide information about the last time an asset was modified, which is actually less information exposure than currently, which provides the last deploy time via any static asset.