[NEW] Slackbridge hidden rooms control

[Hudell]

@RocketChat/core

Closes an item on #8012, merging PR #8053

Attention, this PR is built on top of PR #10205

This PR adds a new setting to determine if a hidden channel should be made visible when there are new messages on it.

Original description:

Extend implements of PR #6299 for hit the suggestions about user's control over "show hidden rooms when unread messages".

[CLAassistant]

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4 out of 5 committers have signed the CLA.

✅ rodrigok
✅ kable-wilmoth
✅ lindoelio
✅ Hudell
❌ Lindoélio Lázaro

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