Rework command `!free` for the new help system.

[ikuyarihS]

Issue

With the newly introduced help systems, the old command !free is no longer relevant.

However, there are will be users who get confused and may post questions in the in-use questions / ask how to and where to get help.

Proposal

We can revamp the !free command to:

• Output a short summary of how to claim a free channel.
• [Optional] Mention the current free channels they can claim.
• [Optional] Show a screenshot of the free channels and what they look like.

[ikuyarihS]

After a discussion, this can also be done by adding a tag to the current tags, and it will be treated as a static tag instead.