Additional partitions

[XaverStiensmeier]

Closes #489

Using the key partitions:

- type: de.NBI small + ephemeral
      image: ^Ubuntu 22\.04 LTS \(.*\)$
      count: 2
      partitions:
        - ephemeral

you can create additional partitions.

This pull request also includes a minor enhancement for the default configurations for slurm and ansible (see #485 and #475 ) by introducing the global keys:

customAnsibleCfg: True # If True, changes in ansible.cfg are kept. Default False.
customSlurmTemplate: True # If True, changes in slurm.j2 are kept. Default False.

this is necessary to ensure users ansible and slurm configs get updated when BiBiGrid updates if they don't use a custom version.