New features

• Add support for installing extensions from repositories.
• Add sdk compile install command for running SDK compile install scripts.
• Generate an SDK package for extensions with SDK dependencies.
• Image external extensions on avocado build.

Improvements

• Export AVOCADO_BUILD_EXT_SYSROOT to extension SDK compile install scripts.
• Redirect persistdir for extension databases.
• Skip SDK compile blocks when running avocado build.

Bug fixes

• Fix ext package --target to properly search config and environment.