RATIS-2384. Add Bill of Materials project

[adoroszlai]

What changes were proposed in this pull request?

Create new submodule ratis-bom (Bill of Materials) for easier dependency management in projects using Ratis.

Before:

<dependency>
  <groupId>org.apache.ratis</groupId>
  <artifactId>ratis-client</artifactId>
  <version>${ratis.version}</version>
</dependency>
<dependency>
  <groupId>org.apache.ratis</groupId>
  <artifactId>ratis-common</artifactId>
  <version>${ratis.version}</version>
</dependency>
...
<dependency>
  <groupId>org.apache.ratis</groupId>
  <artifactId>ratis-server</artifactId>
  <version>${ratis.version}</version>
</dependency>

After:

<dependency>
  <groupId>org.apache.ratis</groupId>
  <artifactId>ratis-bom</artifactId>
  <version>${ratis.version}</version>
  <type>pom</type>
  <scope>import</scope>
</dependency>

https://issues.apache.org/jira/browse/RATIS-2384

How was this patch tested?

CI:
https://github.com/adoroszlai/ratis/actions/runs/21143136602

Also tried it locally by adding ratis-bom to Ozone after mvn -DskipTests install.

[szetszwo]

@adoroszlai , thanks for working on this! Just have a minor comment inlined.

[szetszwo]

This is not needed since the child pom can use the properties in the parent pom.

• See https://maven.apache.org/guides/introduction/introduction-to-the-pom.html#Project_Inheritance_vs_Project_Aggregation

[adoroszlai]

Thanks @szetszwo for the review, patch is updated. However, I've checked some other project BOMs and found that inheriting the main module may not be a good idea. Let me double-check.

[szetszwo]

You are right netty bom does not inherit netty main (i.e. io.netty:netty-parent)

• https://github.com/netty/netty/blob/4.2/bom/pom.xml

[adoroszlai]

Indeed, by ratis-bom inheriting Ratis root POM (ratis), downstream project (Ozone) gets all dependency definitions (e.g. slf4j-simple) from Ratis, which is not desired.

It seems there are two solutions:

1. Make ratis-bom independent (no parent, at least not ratis), and duplicate information like ratis.thirdparty.version. (And the list of Ratis submodules, which is already duplicated in this PR.)
2. Make ratis-bom the parent of ratis, see pattern in Maven docs. This is an additional inheritance layer, but it reduces duplication (including list of submodules).

I think we should now go with (1), since (2) is a bigger change, maybe suitable for Ratis 4.0.

[szetszwo]

+1 the change looks good.