Add flatten-maven-plugin for consumer pom preparation

[rgprajeen]

This PR introduces the flatten-maven-plugin to the project for preparing the consumer POM. The plugin is configured to flatten the POM file during the process-resources phase and clean up during the clean phase. This helps in simplifying and creating a consistent POM structure for consumer projects.

Changes made:

1. Added the Flatten Maven Plugin to the pom.xml:
   • Added the plugin version 1.6.0.
   • Configured the plugin to flatten the POM during the process-resources phase with flattenMode set to oss which retains popular tags in pom.
   • Set up the plugin's clean goal to be executed during the clean phase.
2. Updated .gitignore:
   • Added an entry to ignore the generated .flattened-pom.xml file to avoid committing generated artifacts.

Motivation:

The goal is to prepare the consumer POM by flattening its structure, removing unnecessary information, and simplifying it for downstream usage, especially in the context of distributing and using the POM as a dependency in other projects. With the addition of this plugin during the build process (and the deployment process), the dependencies with version property are resolved and hardcoded. Also, the child-parent module versioning is hardcoded to prevent any kind of ambiguity for the users.

Testing:

• Ensure that the build successfully flattens the POM file during the process-resources phase and the same is used when invoking mvn install locally.
• Verify that .flattened-pom.xml is not tracked in version control.

Additional Information:

No new features or bug fixes were introduced, only a configuration to simplify the POM file for easier consumption in other projects.

[rgprajeen]

@ceki @tony19 Considering the changes are really small and is intended for improvement in user's QOL. Do you mind reviewing this out?

[ceki]

@rgprajeen Thank you for this PR. Being unfamiliar with the flatten-maven-plugin and not wishing to add a layer of indirection to the build process, this PR will not be merged.