Restoring from cache is very slow for large files

In our case, it takes around 2~5 minutes to just tar and untar all the cached files, which account for over 1GB in some cases.

[Tar is currently using `--gzip`](https://github.com/google/wireit/blob/32f805cb2ce82e24ca65f6abeb3cabaf8b64ea2b/src/caching/github-actions-cache.ts#L462) which is slow.
Since there are multiple fast alternatives to the plain gzip, including
- `--no-auto-compress` (No compression)
- `GZIP=--fast` ( -1 Fast flag)
- `Pigz` (Parallel Gzip)
- `Lzop`
- `Zstd`
each one with different tradeoffs.

So the easiest way to cope with different file types, size and use cases would be to provide a way to have the current `tar` flags set as default, and be able to override them through an environment variable or option.