List public servers willing to accept new members

Nobody has claimed this yet.

Get something as user friendly as https://joinmastodon.org/servers and as complete as https://joinmatrix.org/servers/

Important aspects:
- Servers should opt-in to be listed there
- Data updates need to be automated
- "Use at your own risk, this is not endorsed by the m.org foundation" warnings need to be made, all while not being unnecessarily too scary
- Servers listed should agree to some basic principles?

The three filters joinmastodon.org has make sense to me:

- legal structure (is it an individual or an organisation I'm trusting with my account? Helps with the bus factor)
- sign-up speed (is it completely open? Are there manual reviews? Can help determine the quality of the instance and its likeliness to get banned)
- language (useful to get support from admins)

I believe it also makes sense to add a filter for whether the services are paid or free. This might be a criterion that fits in "legal structure" (e.g. "Individual admin", "Non-profit", "Paid service"). Another way to see it is to have a "Support level" filter with "Best effort (single admin)", "Best effort (team)" and "Paid service with support".

No repository files, tests, or entry points are named. Start by comparing the referenced joinmastodon.org/servers and joinmatrix.org/servers pages, then review the listed requirements for opt-in data, automated updates, warnings, principles, and filters; done means an agreed, user-friendly server directory that addresses those requirements.

Written by the indexing model from the issue text.