Order bridges by maturity

Related to #1584

We have cases such as https://matrix.org/ecosystem/bridges/discord/ where (as of today) beta > alpha > stable is in apparently the wrong order. This would be resolved by a more consistent policy about which maturity labels to assign projects.

At the same time, our current code allows things such as https://a15d36a4.matrix-website.pages.dev/ecosystem/bridges/slack/ where
- obsolete projects are featured
- obsolete projects are listed before non-obsolete projects if so defined in the projects .toml

We should let logic in the zola template manage the order, similar to how we order the members of the foundation automatically. We can apply this to obsolete projects already imo. We need to resolve the policy issue for a clear decision on the rest.

Keywords: sort

Start by reviewing the Zola template logic that renders bridge listings, the projects' .toml data, and related issue #1584. The maturity-label policy still needs a clear decision; done means the policy is settled and bridge ordering consistently handles obsolete projects and maturity labels.

Written by the indexing model from the issue text.