DOC-7457: Make team creation workflow easier by adding GIFs

[Rutam21]

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Summary

This PR adds two GIFs to help the users easily find the new team creation options.

• create-team.gif shows how to create a team using the + icon at the top of the Team Sidebar.
• team-create-team.gif shows how to create a new team by selecting the current team name.

Ticket Link

Fixes #7457

• [x] This PR follows the Mattermost Contributing Guidelines.