[Request] `bcftools reheader -s` should also be able to take a string as input

[famosab]

If you only want to rename a sample from one name to another the -s flag should also be able to take just a string as input and not need to create a file.

Current Behavior

-s samples.txt with

samples.txt:

truth

Expected

-s "truth"

[pd3]

It can't be as simple as that. If you provided a non-existent file by mistake, it would silently become a new sample name. We can add a new option. Too bad the choice made in reheader conflicts with the rest of bcftools, where these options are named as

-s, --samples
-S, --samples-file