FEATURE: Allow Fournos to process fjobs from any namespace

[kpouget]

Would be nice to be able to customize the namespace per user where the fjobs run, instead of the current single workflow namespace (psap-automation).

We'll want to support single namespace (for the staging cluster) and any namespace (for the prod cluster)

[kpouget]

One thing to consider is the ability to control the which version of Fournos processes the fjobs.
Can be done with a label or annotation in the NS, matching a parameter of the Fournos instance
Like

• start this fournos with the staging tag
• label this namespace with fournos=staging
  so that I can decide to use the stable or staging instance in my namespace