Deprecate dwave-greedy, dwave-neal and dwave-tabu in favor of dwave-samplers

[arcondello]

With the release of dwave-samplers, we would like to remove dwave-greedy, dwave-neal and dwave-tabu from the SDK.

I propose this be done in three steps:

1. dwave-ocean-sdk~=5.0.0
   • Release pure Python packages neal 0.6.0, greedy 0.3.0, and tabu 0.5.0 that rely on dwave-samplers
     • E.g. Move source code to dwave-samplers dwave-neal#108
   • Include those versions, and dwave-samplers itself, in the SDK
   • In the docs indicate that those solvers are deprecated
   • Update the dwave-examples to use dwave-samplers.
2. dwave-ocean-sdk==6.0.0
   • Release pure Python packages neal 0.6.1, greedy 0.3.1, and tabu 0.5.1 that rely on dwave-samplers and raise a deprecation warning when used
   • Archive the repos for the deprecated packages.
3. dwave-ocean-sdk==7.0.0
   • Remove neal, tabu, and greedy from the dependency list and the docs