[Help Wanted] [PLT-4843] Add CLI tool for deleting channels

[esethna]

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Notes: Jira ticket

We have one for archiving channels, we need to add one for permanently deleting from the database.

Proposed changes:

1. rename existing CLI command platform channel delete to platform channel archive to reflect what it does (delete the channel from UI but leave it in the database).
2. create a new CLI command platform channel delete which permanently deletes a channel from the database (we have one for users and teams)

Channels can be specified by {team}:{channel} using the team and channel names or IDs.

Format: platform channel delete {channels}

Example: sudo ./platform channel delete myteam:mychannel

See related doc for archiving a channel from the CLI: https://docs.mattermost.com/administration/command-line-tools.html#platform-channel-delete
See a PR that added a CLI command for searching for users: #5918

[cpanato]

I will take this one :)

[cpanato]

PR: #6430

[jasonblais]

Thanks! 👍