Allow read-write access to configuration and download directories when installed as a Snap

[richardneish]

We need write access to the $HOME/.config/exercism/ directory for exercism config and $HOME/exercism is the default download directory so we need write access there as well.

This should resolve issue #945

[kotp]

This is only the default installation directory, and should not be hard coded, i think, but should gather that from the configuration file. Otherwise we are likely going to have intermittent permission problems if the user changes the workspace.

[richardneish]

We can allow write access to any subdirectory of $HOME - would that be better?

[kotp]

I suspect that is better. Perhaps the configuration file is not yet written at this point in time, to be able to get the workspace from the configuration.

[ekingery]

It is possible that the ideal solution is for a tighter restriction than $HOME. However, given the installation troubles we've seen, I think it is worthwhile to merge this as-is.

[ekingery]

Thanks for the contribution @richardneish! It should be reflected in the next release of the CLI, which should correspond with the Exercism V3 launch. The build should pass after getting merged with main.

[ekingery]

In order to merge, the build needs to pass. In order for the build to pass, we need to merge the latest changes from main. There was no base branch to merge into, so I created a separate PR for getting this merged: #980