Offer membership for ecosystem and associate members with a dedicated page

Nobody has claimed this yet.

@BramvdnHeuvel was asking in [#ecosystem.forum:matrix.org](https://matrix.to/#/#ecosystem.forum:matrix.org) whether we could provide a link to the website for people to sign up to ecosystem membership. However, we couldn't find a page suitable as the [sign up form](https://cryptpad.fr/form/#/2/form/view/j1+wOJVZWyrDKvGP-G1r-zEOI3a52j5Y22brxhrdcmM/) is linked only from the [main membership page](https://matrix.org/membership/). The existing membership page is heavily centered towards paying members and we reason would be confusing/intimidating to community members. Since they would have to know beforehand that ecosystem membership existed as it is only mentioned in the diagram at the bottom of the page. And because the page is trying to attract a different group of people.

For now, we have linked directly to the form.

Context: https://matrix.to/#/%23ecosystem.forum%3Amatrix.org/%24jfOt5_e4z3kBtFcjusIj47JdwEHIOw5wD0PhfUqyDSg?via=neko.dev&via=matrix.org&via=0x.badd.cafe

Start by reviewing the existing membership page at matrix.org/membership/ and the linked CryptPad signup form. Identify the website entry point and content structure used for membership pages, then define the dedicated ecosystem-membership page around that form. Done means ecosystem members can find the page and reach the signup form without navigating the paying-membership content.

Written by the indexing model from the issue text.