Introduce MCP sample

[geoand]

Currently there is no sample where one can run both the server and the client.
Having a sample would greatly accelerate the journey for users that want to start playing around with MCP.

@jmartisk, @mkouba do you have any examples ready to go that we could add in the samples directory?

P.S. This came up because @kdubois was struggling to get the client and the server to work with each other

[jmartisk]

We have client-server integration tests in langchain4j now, but that obviously isn't useful as samples.
Maybe we could create a sample in this repo, it would probably be two separate projects, client and server (unlike other samples in this repo). I can do it, but maybe somebody has some nice ideas about what it should do :)

[geoand]

We can probably use what @kdubois did in the 06 parts here.
However we ran into what looks like this, so we'll need a fix before adding the sample