the ServiceMeshConsumer should provide a `is_active` method

[adhityaravi]

Enhancement Proposal

Currently the only way to know if a service mesh is connected to a charm or not is using the mesh_type property. which is not not obvious. To overcome this, we need to add a is_active() method or similar that tells if the service mesh connection exists more explicilty

[dstathis]

Yes we should do this. I would prefer to call it enabled() as that seems a bit more clear to me.