Automatic Dependency Deduction

[PengZheng]

Instead of making PushStreams a standalone project (actually we can't), we can combine etcdlib/Promises/PushStreams into Celix, and make the framework optional, so that we can opt to build etcdlib/Promises/Promises+PushStreams alone.

Also automatic dependency deduction can be easily implemented at Conan level. That means if you want PushStreams, Promises will be automatically built for you.

Originally posted by @PengZheng in https://github.com/apache/celix/issues/576#issuecomment-1598382463

I agree. IMO this means:

• Adjusted the cmake files to make the framework and utils lib optional and ensure that bundles can only be build if framework is build
• Introduce a GitHub workflow that only builds etcd, promises and push streams to ensure those libs can be build without the rest of Celix
• Update the building documentation, etcdlib and promises documentation to reflect this.

Originally posted by @pnoltes in https://github.com/apache/celix/issues/576#issuecomment-1599236422