Enhanced Plugin Directory Management in RESTHeart

[ujibang]

Objective:
To enable RESTHeart to load plugins recursively from subdirectories of the plugins-directory.

Current Limitation:
At present, RESTHeart is configured to search for plugins in the directory specified by the plugins-directory configuration option. By default, this is set to ./plugins. It just searches jar files in the directory and won't look into subdirectories. This limitation poses challenges, especially when deploying custom plugins in a Docker environment.

Proposed Solution:
RESTHeart will search for plugins in the plugins-directory and recursively in its subdirectories (up to two levels deep).

Use Case Scenario:
In a Docker deployment scenario, users often need to deploy custom plugins. The current system requires the use of Docker volume mappings for each custom plugin or its dependencies, like this:

$ docker run -rm -p 8080:8080 -v custom-plugins.jar:/opt/restheart/plugins/custom-plugins.jar softinstigate/restheart

However, remapping the /opt/restheart/plugins directory to include custom plugins risks overwriting the standard plugin JARs (e.g., restheart-graphql.jar) that come with RESTHeart. The challenge is amplified when a plugin has several dependencies, necessitating multiple Docker volume mappings.

Benefits of the Proposed Change:

1. Flexibility: Allows separation of custom and standard plugins into different directories.
2. Simplified Deployment: Reduces the complexity in Docker environments by minimizing the need for multiple volume mappings.
3. Maintainability: Eases the process of updating and managing custom and standard plugins independently.

Implementation Considerations:

• Ensure backward compatibility, where the system can still function with a single directory specified.
• The plugin loader should gracefully handle any conflicts or issues arising from plugins in different directories (e.g., duplicate plugins, version conflicts).
• Update relevant documentation to reflect these changes and provide examples for new and existing users.

Detailed Documentation:
To be developed, detailing the technical implementation, configuration changes, and examples of usage in different deployment scenarios.

[ujibang]

done, available in v7.7.0