Micro ocdav

[butonic]

This PR adds a new pkg/micro package that exposes the internal ocdav http handler as a go micro service. For testing pkg/micro/ocdav/cmd/main.go can start the service standalone.

• add auth, ctx, log, middlewares
• add tracing middleware
• add more config options

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[kobergj]

@wkloucek could you check tracing commit?

[micbar]

Code looks good IMO. It only adds a new way of starting the ocdav service whithout changing existing behavior.