DWaveCliqueSampler should have solver property at top level

**Description**
DWaveCliqueSampler is not a composite with a child solver so I'd expect it to have a `.solver.name` property at top level analogous to DWaveSampler.:
```
>>> sampler_clique.solver.name
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
in
----> 1 sampler_clique.solver.name

AttributeError: 'DWaveCliqueSampler' object has no attribute 'solver'
```

**To Reproduce**
See above.

**Expected behavior**
I think `.solver.name` should be copied to the top level.

**Environment:**
- OS: Win
- Python version: 3.7

**Additional context**
You can do this:
```
>>> sampler_clique.child.solver.name
Out[8]: 'DW_2000Q_6'
```