Extensible job configurations

[enkore]

A bit like Jenkins: add actions before/after the actual archive creation. Allow plugins to provide "blocks".

This is quite vital. It allows to prepare the system for a backup, eg. by creating a FS snapshot or pausing processes.

[enkore]

Ie. similar to the steps of a schedule:

But conceptually different: schedule gathers actions across clients and repositories; "blocks" in a job configuration would be specific to that client and job config.

Ie. a typical schedule would be "daily backup" which creates a daily snapshot of all clients, checks the repo, and prunes. Blocks in a job config would be used to eg. dump a DB before creating an archive of the dump, then creating an archive of / or some data dir or whatever.