Update notification banner and global nav

[emdecr]

Summary

This PR adds the 9.0 announce blog to the notification banner, and updates the global nav to align with mm.com.

@cwarnermm – Feel free to adjust the footer links and I'll mirror the changes on mm.com. Will add more reviewers once we're zipped up.

Thank you!

[github-actions[bot]]

Newest code from emdecr has been published to preview environment for Git SHA 818822ea8faa235c752a3ef50a7aa67ee9e2538e

[github-actions[bot]]

Newest code from emdecr has been published to preview environment for Git SHA 818822ea8faa235c752a3ef50a7aa67ee9e2538e

[github-actions[bot]]

Newest code from emdecr has been published to preview environment for Git SHA 818822ea8faa235c752a3ef50a7aa67ee9e2538e

[github-actions[bot]]

Newest code from emdecr has been published to preview environment for Git SHA 818822ea8faa235c752a3ef50a7aa67ee9e2538e

[cwarnermm]

@emdecr - Let's apply the 2 header updates proposed via x:

• Let's update the Academy link to point to: https://academy.mattermost.com/
• Let's update the Release Notes link to: https://docs.mattermost.com/guides/changelogs.html

And just to confirm, the dev docs site footer is far simpler than the docs footer intentionally?

[github-actions[bot]]

Newest code from emdecr has been published to preview environment for Git SHA fa091374e1ba933792472b7b3ef31856df1d8d69

[emdecr]

@cwarnermm Yep – I don't think there's ever been a footer mirror (of docs/mm.com) on this site since I've been here.

[emdecr]

@nat-gunner For review - nav changes for 9.0 - TY!

[cwarnermm]

@emdecr - phew! For a moment I thought I was mis-remembering one! :)

[github-actions[bot]]

Newest code from cwarnermm has been published to preview environment for Git SHA fa091374e1ba933792472b7b3ef31856df1d8d69