Showcase vlingo-schemata integration

[wwerner]

Developped alongside vlingo/xoom-build-plugins#2
See vlingo/xoom-schemata#105

[VaughnVernon]

@wwerner 👍 I wish this could be less verbose, similar to the actorProxy entries. Is it possible?

[wwerner]

I understand and find it too verbose as well.
However, I fould most alternatives too prescriptive:

• Tie maven project version to the schema version - users can still do that using maven properties, but are not forced to
• Parse the reference and version from the file name - feels brittle and too prescriptive

What we could do:

• Let schemata figure out the previous version on the server side - this would benefit the UI as well and fit into the semantic versioning validation task
• Make the source field optional and default to src/vlingo/schemata/<schema name from the reference>.vss.

In combination this would allow us to write

 <schemata>
   <schema>
     <ref>Vlingo:examples:schemata:SchemaDefined:0.0.1</ref>
     <!-- uses the default source file from the reference -->
   </schema>
   <schema>
     <ref>Vlingo:examples:schemata:SchemaPublished:0.0.1</ref>
     <src>some/other/weird/file.foo</src> <!-- but can be overridden -->
   </schema>
 </schemata>

I'd implement the second part now, then merge this PR and rework config and examples after the first part is implemented on the server side.
Ok?

See ⬇️ & vlingo/xoom-build-plugins#4

[VaughnVernon]

In combination this would allow us to write

 <schemata>
   <schema>
     <ref>Vlingo:examples:schemata:SchemaDefined:0.0.1</ref>
     <!-- uses the default source file from the reference -->
   </schema>
   <schema>
     <ref>Vlingo:examples:schemata:SchemaPublished:0.0.1</ref>
     <src>some/other/weird/file.foo</src> <!-- but can be overridden -->
   </schema>
 </schemata>

I'd implement the second part now, then merge this PR and rework config and examples after the first part is implemented on the server side.
Ok?

@wwerner Ok, good. Let's go with this. Thanks!