Add Provide-Capability for declarative services bundle

To allow bundles to declare that they need declarative services, a Provide-Capability should be defined on the DS bundle such that clients can depend on it, for example:

Provide-Capability: osgi.extender;osgi.extender="osgi.service.component";version:=1.1.0

This would allow clients to require that there be a Declarative Services bundle without actually declaring a package dependency:

Require-Capability: osgi.extender;filter:="(&(osgi.extender=osgi.service.component")(version>1.0.0))"

The name of the declarative services component isn't well defined but osgi.service.component or osgi.declarative.services might be used.