Use zstd instead of gzip where possible

First commit:

Visible size reduction and minor performance improvement at no cost.

rootfs measure:

2022-07-27 11:15:16.235268: 475MB downloaded in 111.59s (4.26MB/s)
2022-07-27 15:07:40.984857: 425MB downloaded in 85.57s (4.97MB/s)

So let say approx. 95s vs 85s if we assume 5MB/s, which can bring us 10s speedup...

Don't count the fact that compression and decompression are faster than with gzip.

Second commit:

Size difference approx. 48 to 46 M, compression 4x time faster, decompression 8x faster 4s -> 0.5s on my PC.

Replaces original !17769 (closed)