Add option for JSON formatted output (#324)

* Spit out JSON results at the end of a build

* Mark `--output_json` as conflicting with `--verbose`

* Override verbosity to `quiet` when outputting JSON

* Update tests to include `OutputType` param

* Temporarily please Clippy

* Add some logging

This is gonna fail, but I want to see what the CI has to say.

* Remove TODO so that format CI step passes

* Return result from `serialize_json`

* Make JSON test a sanity check

* Mention this PR in the CHANGELOG

* Implement `Default` for a few build options

* Address Clippy's `too_many_arguments` lint

* Use `ExecuteArgs` in tests

* Make `manifest_path` field public instead

Clippy was complaining about `dead_code` when building
in non-test mode, so I'm going with this instead.

* Apply suggestions from code review

Co-authored-by: Michael Müller <[email protected]>

* Sanity check `BuildResult'` JSON serialized form

* Add `execute()` test back

* Import `OutputType` in tests

Co-authored-by: Michael Müller <[email protected]>