Create default fallback

[jacobtomlinson]

Added a default lookup location for create_cluster(). If you fail to specify the path to a valid spec it will try and find it at dask-cluster.yaml.

>>> import dask_ctl.lifecycle
>>> dask_ctl.lifecycle.create_cluster()
DaskClusterConfigNotFound: Unable to find dask-cluster.yaml

You can also set the local_fallback=True option to start a LocalCluster if a spec file is not found.

>>> import dask_ctl.lifecycle
>>> dask_ctl.lifecycle.create_cluster(local_fallback=True)
LocalCluster(3ce576d4, 'tcp://127.0.0.1:8787', workers=4, threads=12, memory=93.02 GiB)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (afc0e5c) 71.14% compared to head (d00ace7) 72.01%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #65 +/- ## ========================================== + Coverage 71.14% 72.01% +0.86% ========================================== Files 10 11 +1 Lines 357 368 +11 ========================================== + Hits 254 265 +11 Misses 103 103 ```

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