[Documentation] Resume Experiment feature

[andreyvelich]

/kind feature

We implemented new feature: resuming Experiment from volume: #1275.

We should document that Experiment can be resumed after completion.
In Experiment yaml user can specify 3 different resume policies, we should explain what does it mean.

As well, after this: #1291. PVC and PV settings can be controlled via Katib config.
We should explain it.

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[andreyvelich]

/area release
/priority p1