Generate code during maven build (protobuf/omt schema)

[msbarry]

Ideally we wouldn't check generated code (protobuf and OMT schema) into git and instead generate it on the fly as part of the maven build.

Related to #109

[wipfli]

scripts/regenerate-openmaptiles.sh should be easy with the formatting in #122.

scripts/regenerate-protobuf.sh gives me an error:

➜  planetiler git:(eclipse-formatter) ✗ scripts/regenerate-protobuf.sh     
+ echo Regenerating...
Regenerating...
+ protoc --java_out=planetiler-core/src/main/java/ planetiler-core/src/main/resources/vector_tile_proto.proto
scripts/regenerate-protobuf.sh: line 5: protoc: command not found

[wipfli]

With sudo apt install -y protobuf-compiler on ubuntu, I can also run the protobuf generation script.