Mattermost-server: Document sql store 'SqlTeamStore' methods (Task 6)

[mattermod]

We want to improve our internal API documentation using godoc to ease the
development process for everybody.

This Help Wanted issue is to add the documentation to the following methods
(file: (https://github.com/mattermost/mattermost-server/tree/master/store/sqlstore/team*store.go)):

• SqlTeamStore.PermanentDelete
• SqlTeamStore.RemoveAllMembersByTeam
• SqlTeamStore.RemoveAllMembersByUser
• SqlTeamStore.RemoveMember

An example of already migrated methods can be found here:

• https://github.com/mattermost/mattermost-server/pull/13896

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JIRA: https://mattermost.atlassian.net/browse/MM-23001

[FlaviaBastos]

Opened pull request https://github.com/mattermost/mattermost-server/pull/14785 for this issue.