Add messages context in the app side nav

[wpalani]

Proposed changes

Add a new container()->plugin()->id . '-app-nav' context to the module API, this context can be used by the brand plugins to retrieve notifications that can be displayed in the app nav.

** Tests might be failing now as this change requires an update in the brand plugin's app to render the messages in this context in the side nav.

This PR addresses this internal ticket: https://jira.newfold.com/browse/PRESS0-1151

Demo

nav-message-demo.mp4

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• Linting and tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[wpscholar]

Should this be container()->plugin()->id . '-app-nav'?

[wpalani]

Good catch! fixed.

[wpscholar]

@wpalani It looks like all the tests are failing due to a failing site gen test. I think we'd be fine to merge, but if there is an issue with the site gen tests, we should have the appropriate team look into why those are failing.