DOC-7531: Join and leave channels page needs animated GIFs for mobile app workflows

[Rutam21]

Summary

This PR adds visual workflows for the Mattermost mobile app tab on the Join and leave channels page

Ticket Link

Fixes #7531

• This PR follows Mattermost Contributing Guidelines.

[mattermost-build]

Hello @Rutam21,

Thanks for your pull request! A Core Committer will review your pull request soon. For code contributions, you can learn more about the review process here.

[Rutam21]

@cwarnermm Please review and suggest changes, if any. Thanks.

@lindy65 Please add this to my queue for QA Testing once the reviews are complete. Thank you.

[lindy65]

Assigned to you for testing @Rutam21 - will still count towards Hacktoberfest as it was before end of day on 31 Oct

[github-actions]

Newest code from Rutam21 has been published to preview environment for Git SHA 0bda9ed

[Rutam21]

The changes are tested in the preview environment and they reflect properly.

• The Join and leave channels page has now 6 new workflow images under the mobile tab for visual learners.

Please refer to the screenshots below as a confirmation.

Current Docs Page [Join and leave channels]

Join a channel Section

Leave a channel section

Preview Environment Page

Join a channel Section

Step 1

Step 2

Step 3

Leave a channel section

Step 1

Step 2

Step 3

Step 4

[ Awaiting final review from @cwarnermm ]

cc: @lindy65

[lindy65]

Thanks for testing @Rutam21 - counted towards Hacktoberfest

[cwarnermm]

Thank you, @Rutam21!