Deprecate BackendV1

[1ucian0]

Summary

Time to deprecate BackendV1 in favor of Target (for hardware description) and primitives (for execution). We should still keep BackendV2 as a supported alternative.

This requieres:

• Deprecate Qobj and assemble #12649
• Deprecate fake backends based on BackendV1 #12660

once this one is merged, the rest of the _assemble code needs to be cleaned. Hopefully, it can be done after the release of this PR.

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[mtreinish]

What's more important to me than the actual backendv1 abstract class definition is deprecating the things it uses, specifically the models objects in: https://github.com/Qiskit/qiskit/tree/main/qiskit/providers/models and also qobj and assembler modules

[1ucian0]

What's more important to me than the actual backendv1 abstract class definition is deprecating the things it uses, specifically the models objects in: https://github.com/Qiskit/qiskit/tree/main/qiskit/providers/models and also qobj and assembler modules

done in #12649

[wshanks]

#12649 deprecates qobj and assemble, but what about the models in qiskit/providers?