[follow-up] Change SEP process to allow for alignment on requirements beforehand #1435

From the MCP Core Maintainer meetup:

We currently ask contributors to write full outlines SEPs. These include both problem, statement as well as proposed solution. However for large changes this makes discussion difficult and most importantly requires authors to spend a lot of time on writing a proposed solution without knowing if Core Maintainer are aligned with the problem.

We want to improve the process to allow SEP authors to ask for alignment before committing to writing a full SEP.

This likely fits nicely into #1434 . Working groups should help with this alignment and rely on the core maintainers only when in doubt about a direction.