Update help message for dbfix

Related to #918 (closed) , I think the dbfix fixes the jobs database only, not the main database of Autosubmit?

I had a look at the source code, and it appears to move and re-create the job_packages_xxx DB, not the main DB (the one in autosubmitrc).

This is the current (master) help of dbfix:

$ autosubmit dbfix --help
usage: autosubmit dbfix [-h] expid

historical database functions

positional arguments:
  expid       experiment identifier

options:
  -h, --help  show this help message and exit

I think we should document which DB will be fixed.