Resolve #600 ssh_filter_btrbk.sh allow zstd --adapt

[zwimer]

This PR fixes:

1. Fixes Update ssh_filter_btrbk.sh to allow stream_compress with adaptive compression #600 by allowing --adapt to be whitelisted for zstd instead of a specified compression level
2. Expands the existing compression regex to match compression level [0-9]{1,2} instead of just [0,9]. This allows users to use compression levels higher than 9, like zstd -c -10
3. There were 5 tabs in the file that was otherwise formatted with spaces- it fixes that