[Feature/extensions] Add framework support for default extension points

[saratvemulapalli]

Add extension framework support for default extension points

OpenSearch/server/src/main/java/org/opensearch/plugins/Plugin.java

Line 90 in 2146827

public abstract class Plugin implements Closeable {

• getFeature - Implement a custom feature and respond to cluster state API.
• createGuiceModules - Implement node level dependency injection modules via Guice.
• getGuiceServiceClasses - Node level services which will be automatically called with node state changes.
• createComponents - Custom component implemented and its lifecycle being managed by OpenSearch.
• additionalSettings - Implement additional node level settings.
• getNamedWriteables - Custom parsers the plugin would use for transport messaging.
• [Feature/extensions] getNamedXContent - Add support for extensions #3379
• onIndexModule - Index level extension point, called before an index is created.
• getSettings - Implement additional cluster level settings.
• getSettingsFilter - Implement additional cluster level settings filter.
• getSettingUpgraders - Implement setting upgraders.
• getIndexTemplateMetadataUpgrader - An extension to modify index template metadata on startup.
• getExecutorBuilders - Implement custom thread pools for executions.
• getBootstrapChecks - Add additional bootstrap checks when OpenSearch node initializes.
• getRoles - Implement additional DiscoveryNodeRole’s.
• getAdditionalIndexSettingProviders - Implement additional index level settings for newly created indices.