Make "servlet server" use case easier to consume

[onobc]

We need to either make the "servlet server" use case easier to consume or update docs a bit to spell out what needs to be set/added for it to work.

Originally posted by @onobc in #97

[dsyer]

I'd be in favour of adding a starter including spring-boot-starter-web and grpc-servlet-jakarta.

[onobc]

I'd be in favour of adding a starter including spring-boot-starter-web and grpc-servlet-jakarta.

Exactly where I was headed 💯 (also plays well w/ #90)