Support custom config file locations via environment variables

[NorthIsUp]

This adds support for a custom config file location via the new $MACKUP_CONFIG var or by checking for $XDG_CONFIG_HOME.

It searches for config files in the following order:

• ~/.mackup.cfg
• $MACKUP_CONFIG
• $XDG_CONFIG_HOME/mackup/mackup.cfg
• ~/.config/mackup/mackup.cfg

if none of these exist ~/.mackup.cfg is created and used

[con-f-use]

How has that not been merged yet? Seems like's been a very hot topic for a long time https://github.com/lra/mackup/issues/473 https://github.com/lra/mackup/pull/632 https://github.com/lra/mackup/pull/1318 https://github.com/lra/mackup/pull/1694 https://github.com/lra/mackup/issues/1509 https://github.com/lra/mackup/pull/1987

[con-f-use]

pretty plz.

[lougreenwood]

Seems like a pretty straight forward & sensible PR for a long-requested feature. @lra any thoughts on this PR? Thanks! 🙏

[coquizen]

Agreed, this should be implemented. Those concerned with their config settings are often concerned with organizing where those config files are stored.