Add API documentation for guest api new endpoints

Description

Document the new endpoints added in the PRs:

  • pr-mattermost-server-10792

  • pr-mattermost-server-10791

QA Test Steps

No testing required.

Reporter

None

Mana

None

Assignee

Jesús Espino

QA Assignee

None

Reporter

Jesús Espino

Epic Link

None

Fix versions

Mattermost Team

Platform

Sprint

None

Labels

None

QA Testing Areas

None

GitHub Issue

None

Components

None
Configure