Add Rosetta 2 feature toggle for Silicon Mac

Adds a new config sdkman_rosetta2_compatbile to .sdkman/etc/config for switching on/off Rosetta 2 compatibility mode:

• is exclusive, either x86_64 or arm64
• chooses x86_64 + Rosetta 2 by default
• can be switched to false to use native JDKs
• Only Azul Zulu arm64 JDKs available
• interim solution until more vendors release native arm64 JDKs

Silicon Mac support and env install subcommand

This release contains several new features and some other improvements and fixes:

• platform inference for ARM64 Mac architecture
• adds sdk env install subcommand
• display helpful tip when version not found for platform
• only sources .sh files on initialization

Sensible return codes and Flush All

This release has two new improvements:

• omitting the qualifier in the flush command will flush all directories (not version or broadcast)
• sensible return codes are returned for scripting situation, with appropriate test coverage

Support ARM64 Linux architecture

• Supports aarch64 Linux architecture.

Minor bug fix release

Fixes minor issue #779

Minor improvements and performance enhancement

• Replace $(cat file) invocations with $(< file) for better performance.
• Use relative path for current symlink to version directory.
• Improve handling of secure curl downloads.
• Remove unused legacy bash workarounds