Implement Jib plugin extension framework

[chanseokoh]

Umbrella issue for Jib plugin extension framework.

The framework will enable anyone to easily extend and tailor the Jib plugin behavior to their liking.

Quote from #1962 (comment):

As we are getting numerous feature requests to Jib (many of which are often very specific to certain use-cases, don't align well with Jib's model or intentions, are too complex to support without polluting our codebase or configuration with special code, etc.), we decided to introduce an extension framework to Jib rather than trying to implement all of them one way or another. With the extension system, anyone will be able to extend and/or modify Jib's behavior relatively easily and have a fine-grained control over most of the aspects of image building. I think that will cover most of such issues and FRs, including this one.

Check out the new Jib Extensions Portal for a collection of extensions!

Build Plan Specification and API

• proposal: Container Build Plan API specification (Container Build Plan specification #2312, Update arch/OS properties in build plan spec #2329, Update Build Plan API to accept file ownership in layers #2494)
• set up project for Build Plan API (Set up jib-build-plan sub-project #2324, Fix jib-build-plan metadata #2358)
• move essential Jib Core classes into Build Plan project (Copy essential classes into jib-build-plan #2328, Remove Guava dependency from certain core API classes #2327)
• migrate Jib Core library to use migrated classes (Migrate core classes in jib-core to classes in jib-build-plan #2331, Migrate and deprecate LayerConfiguration and LayerEntry #2334, Migrate deprecated LayerConfiguration and LayerEntry usage #2337)
• define Build Plan Java API (Add ContainerBuildPlan as Build Plan API interface #2338, Convert LayerObject to interface #2347, Return copies instead of exposing internal collections / and more #2366)
• conversion methods in Jib Core: JibContainerBuilder <--> Build Plan API (Build plan adapter methods for JibContainerBuilder #2353)

Plugin Extension API

• set up project for common extension API base (Set up extension API sub-project for Jib Maven plugin #2368)
• set up project for Maven plugin extension API (Set up extension API sub-project for Jib Maven plugin #2368, Sync Maven API versions in project build #2359)
• set up project for Gradle plugin extension API (Set up sub-project for Gradle plugin extension and define extension API #2400)
• define Maven extension API (Add Maven plugin extension API #2380)
• define Gradle extension API (Set up sub-project for Gradle plugin extension and define extension API #2400)

Extension Framework

• scaffold common extension execution infrastructure (Scaffolding plugin extension execution #2393, Always set image format configuration #2379, Catch runtime exceptions from extension execution #2474)
• load and run Maven extensions (Run Maven plugin extensions #2397)
• load and run Gradle extensions (Run Gradle plugin extensions #2411)
• design extension configuration option (Add and enable new plugin extension configuration in Maven #2420)
• apply configuration option for Maven extensions (Add and enable new plugin extension configuration in Maven #2420)
• apply configuration option for Graldle extensions (Add and enable new plugin extension configuration in Gradle #2431)
• enable extension-defined custom configuration (Enable extension-defined custom configuration #2464, Show helpful and actionable messages to guide the user to correct extra extension config #2473)
• ...
• ...
• ...
• enable simplified extension configuration usage
• ...

Specification and API Publication (4 Artifacts)

• set up release scripts and Kokoro/Rapid pipeline (Set up Plugin Extension API releases (4 artifacts to Maven Central) #2427)
• publish Build Plan and Extension Common (Build plan release v0.1.0 #2441, Extension common release v0.1.0 #2442)
• migrate Plugins Common and Maven/Gradle Extension APIs to depend on published artifacts (Use published Jib Plugins Extension dependencies #2443)
• publish Maven/Gradle Extension APIs (Gradle extension release v0.1.0 #2444, Maven extension release v0.1.0 #2445)
• migrate Maven/Gradle Jib plugins to depend on published artifacts (Migrate jib-{maven|gradle}-plugin to use published extension API #2446)

Review Items

• check multiple occurrences of the same extension on the classpath

Preparatory/intermediate refactoring and fixes: #2344, #2349, #2378, #2412, #2414, #2432, #2472

[chanseokoh]

I'll close this issue to signal to the public that the extension framework is fully implemented and working. For a few remaining issues, I'll file new issues for tracking.

For those interested in using and writing Jib extensions, check out the new Jib Extensions Portal.