Replace rocketchat with matrix

We're using https://github.com/helm/charts/blob/master/stable/rocketchat which is deprecated since Nov 2020, and won't get updated anymore. It ships rocketchat 3.6.0.

On https://artifacthub.io/ there are two other 3rd party rocketchat charts and at least the Dteam rocketchat chart seems to be actively mantained and ships a recent rocketchat version (3.13.2). Latest rocketchat release is 3.14.5

Edited by Varac
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