Standardize file locations for supporting files

[sean-zheng-amazon]

Coming from opensearch-project/opensearch-plugins#127.

We should standardize the file location across plugins by implementing following conventions:

• All supporting files for plugins should stay within the plugin's own folder: /plugins/my-plugin
• Within plugin's folder, we recommend following directory structure:
  • ./config: config files
  • ./bin: executables
  • ./lib: for plugins that use native libraries (e.g. libKNNIndexV2_0_11.so)
  • ./install: scripts called to bootstrap the plugin before first use.
  • ./docs: document files
  • ./certs: certificates for the security plugin
  • ./data: test/demo data
• All scripts should come in *nix and .bat flavors, should use OpenSearch's defaults for environment variables like $JAVA_HOME, so users can override these but don't need to specify them by default. Scripts should have 0755 permissions by default.

[lezzago]

Closing as the Alerting plugin is following this format