Convert public channels to private channels page needs animated GIFs for mobile app workflows

[Rutam21]

Context

To help visual learners learn how to perform tasks using the Mattermost mobile app, add visuals and short animated GIFs on the Convert public channels to private channels page.

Parent Issue: #6657

Docs Request

• Add appropriate visuals/GIFs for all the steps in the Convert public channels to private channels section under the mobile app tab.

Additional Notes

• Use the latest Mattermost mobile app and the standard Mattermost Denim theme to capture all workflows.
• Avoid drawing lines, arrows, boxes, or callouts on images.
• Don't forget to include ALT Text descriptions for all new image assets.
• Use existing docs pages with images as a starting point for code guidance. The Docs team can help provide RST syntax support for publication.
• Save static image files in PNG format within the docs repository's /images directory.

QA Validation Criteria

In a generated docs preview:

• Visiting the docs page results in appropriate new mobile-specific screenshots in each subsection from the Mobile tab.

[Rutam21]

@cwarnermm Please assign this ticket to me. Thanks.