Add attributes to databricks_cluster_policy data source

[840]

Changes

Adds the following attributes to the data source cluster policy:

• description
• policy_family_id
• policy_family_definition_overrides
• is_default

Closes #1947

Tests

I have modified the TestDataSourceClusterPolicy to test the cluster policy data structure using the new attributes.

• make test run locally
• relevant change in docs/ folder
• covered with integration tests in internal/acceptance
• relevant acceptance tests are passing
• using Go SDK

[codecov-commenter]

Codecov Report

Merging #2351 (f8a116d) into master (130c52d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2351   +/-   ##
=======================================
  Coverage   88.58%   88.59%           
=======================================
  Files         140      140           
  Lines       11546    11554    +8     
=======================================
+ Hits        10228    10236    +8     
  Misses        879      879           
  Partials      439      439           

Impacted Files	Coverage Δ
common/version.go	80.00% <ø> (ø)
policies/data_cluster_policy.go	100.00% <100.00%> (ø)

[alexott]

code looks good

[alexott]

Acceptance tests are failing, but on not related tests (timeout)