Improve selectbox datetime formatting for existing datetimes for mount/unmount actions

Currently when we open the configurations page and its platforms & devices tab, we get a select list with several existing dates:

This show the moments in that a mount or unmount actions happened.

The format of the times there should be improved.

It makes more sense to show something like 2021-12-12 09:09 - Mount Container_N which is more what people are used to.

Important

Should be included in #97 (closed)