Heads up, generated PB files no longer in source code

[Viraj Jasani <vj...@apache.org>]

Hi,

With PHOENIX-6282 in, we no longer have generated PB Java
files available in source code and they are expected to be 
generated inline with mvn build, for both: master and 4.x.

What this means for us is after rebasing our fork with
upstream, IDE might start complaining about missing
generated PB files, hence it is recommended to run
mvn clean build to generate PB files, and for IDE,
we might have to invalidate cache (or reimport the project)
after clean build (one time activity).

For any in progress PR with updates on .proto or introducing
new .proto, you will most likely have merge conflicts. While
resolving them, the only change expected from dev is updating
.proto file only and let go of generated PB Java code. In fact,
phoenix-core no longer has "org.apache.phoenix.coprocessor.generated"
package in source code.
Going forward, dev testing will always require mvn clean build
if any of .proto files are updated as part of the patch.
Thanks

- Viraj