feat(java): Put java and spark libraries within a directory `maven-projects` to help easily manage and extend the multi-module maven projects

[acezen]

Reason for this PR

Since we would split the java library to multi-module project and spark rely on one of the modules 'info', it's better to put java and spark libraries within a directory. That help easily manage and extend the multi-module maven projects

What changes are included in this PR?

• Put java and spark libraries within a directory maven-project
• Update the related link and document

  Are these changes tested?

  No

[acezen]

This PR will make the branch-feat-spark-java-info-refactoring branch easily to merge into the main.

[acezen]

Hi, @Thespica @SemyonSinchenko, This change is related to Java and Spark, it's better to get some review or advice for the change.

[acezen]

For module in root pom, I consider it should be module name, rather than directory name.

A better solution is unifying the directory name and module names.

https://github.com/apache/incubator-graphar/blob/b33c1f0f36246fa45761fb5d122f869d18432a7e/pom.xml#L33

https://github.com/apache/incubator-graphar/blob/b33c1f0f36246fa45761fb5d122f869d18432a7e/spark/pom.xml#L34

https://github.com/apache/incubator-graphar/blob/b33c1f0f36246fa45761fb5d122f869d18432a7e/java/pom.xml#L35

Make sense to me, I will update it to the directory name.

[acezen]

hi, @Thespica, the module name has been unify with directory name.

[acezen]

LGTM~ Besides, #467 can be closed, right?

yes, #467 is solved by this PR.