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

With the release of [dwave-samplers](https://github.com/dwavesystems/dwave-samplers), we would like to remove [dwave-greedy](https://github.com/dwavesystems/dwave-greedy), [dwave-neal](https://github.com/dwavesystems/dwave-neal) and [dwave-tabu](https://github.com/dwavesystems/dwave-taby) 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. https://github.com/dwavesystems/dwave-neal/pull/108
* Include those versions, and dwave-samplers itself, in the SDK
* In the docs indicate that those solvers are deprecated
* Update the [dwave-examples](https://github.com/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