azd extension EngSys

[danieljurek]

A lot of the existing CLI logic can be re-used, but there are many CLI/packaging-specific steps that need to be removed.

Work:

@wbreza

• Create release-ext.yml template similar to release-cli.yml template but uses parameters to know where the extension path and a release-ext-demo.yml file that does release for demo extension
• Create ext-build-and-test.yml files to do build and testing
• Create cross-build yml file
• Output binaries to artifacts similar to CLI build (e.g. azd-<platform>-<arch>)

@danieljurek

• Create pipeline
• Generalize sign.yml
• Generalize publish.yml (does all release and upload work)
• Wire up sign+publish into release-ext.yml