Do not overwrite the contents of mkinitcpio.conf

[ventureoo]

• This fix issue: N/A

PR Description:

After installation is complete, user may want to edit /etc/mkinitcpio.conf at will and may encounter a mismatch between the default configuration examples and what it has after installation since archinstall does not just change some values, but completely overwrites contents of the file removing all comments and other options. This PR fixes this by editing only parameters specified in code like hooks/modules/etc.

Tests and Checks

• [x] I have tested the code!
  (did not test install process, but tested the operation of a separate mkinitcpio function on default mkinitcpio.conf file).