Support SDKMAN RC files

[dmikusa]

Summary

This PR includes support to read a '.sdkmanrc' file if it's present at the root of the application.

The version order is (from lowest to highest priority): Java buildpack default (11), Maven MANIFEST.MF properties, SDKMAN RC file, and BP_JVM_VERSION. Higher priority locations override lower priority locations. Note that Maven MANIFEST.MF entries only apply to pre-compiled assets (as MANIFEST.MF won't exist in a source build) and SDKMAN RC only applies when building from source (as it won't likely exist in a pre-compiled asset).

The buildpack will read the '.sdkmanrc' file, look for the 'java' component (if multiple, it picks the first one), and takes the major Java version indicated in the entry. It ignore minor/patch versions, it also ignores the vendor (the vendor is set based on the buildpack you use). The buildpack ignores other components.

Use Cases

Developers commonly use the SDKMAN tool. It can write a .sdkmanrc file which can be used to indicate the Java version that's required by the application. The buildpack can read this file and use it to know which Java version to install.

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).