[Webapp] Backport 5.16 desktop notifications updates to 5.15, 5.14 and ESV (5.9)

Description

In order to ensure that Desktop Notifications continue to work following an upgrade to Desktop v4.3.0 (due to security related updates), changes needed to be made in the Webapp (v5.16). These changes now need to be ported back so that anyone updating to Desktop v4.3.0 that is still on 5.15, 5.14 and ESV (5.9) will continue to have fully functional Desktop Notifications.

QA Test Steps

One note for QA: there shouldn't be notification compatibility issues if servers are upgraded to the backported server versions but still using v4.2 or earlier, but QA should verify.
No testing required.

Reporter

None

Status

Mana

4

Assignee

Dean Whillier

QA Assignee

Steve Mudie

Reporter

Dean Whillier

Epic Link

None

Mattermost Team

Sustained Engineering

Sprint

None

Labels

None

QA Testing Areas

Notifications - Desktop

GitHub Issue

None

Components

None
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