Parse Java distribution from .sdkmanrc

[mlschechter]

Description:
Given that the action now supports reading the Java version from the .sdkmanrc file, it would be advantageous to read a default distribution from that file as well. SDKMan uses distinct suffixes for each distribution to simplify mapping.

Justification:
Removes the need for users to duplicate the distribution information into their workflow.

Are you willing to submit a PR?
Maybe? Depends on the level of effort :)