Add Spring Boot starter for Supabase with security & database support

[matthewadams]

Please add a Spring Boot starter for Supabase, including the following features:

• Autoconfiguration of Spring Security for authentication and authorization,
• Autoconfiguration of PostgreSQL data source information given Supabase project URL, anonymous key & service key.

There is some prior art for this at https://github.com/tschuehly/htmx-supabase-spring-boot-starter from Thomas Schühly, AKA @tschuehly.

Bonus points for figuring out how to provide a local or in-memory Supabase instance for integration testing, since Supabase supports self-hosting.

This could lead to an umbrella subproject of "BaaS" (backend-as-a-service) support ("Spring Boot BaaS"?) with Supabase as a supported provider, along with others, like Firebase, etc.

[bclozel]

Plenty of well-known and well-supported starters are third party starters and we happily list them on our dedicated page. We don't have plans to invest in this space right now. As a first step, building a community around htmx-supabase-spring-boot-starter is a good idea.