Feature/generalise commit and extensions

[alexjbush]

Description

This PR aims to introduce a simple 'Extension' system allowing users to bring their own extensions to use with DataFlows. This 'Extension' system allows bespoke metadata to be added to the flow, and a mechanism for manipulating a flow before it is executed.

The following existing functionality has be modified to use this extension system:

• Commit functionality
• Cache as Parquet

I have also changed the functionality of the Cache action to:

• Only cache is a label is used as input for more than one action
• Ignore any tags that are active when the cache is applied (the tag state of the underlying action that is intercepted is still preserved)

I have also moved the commit, and spark actions into the package object.

None of the above changes should be breaking.

Fixes #54

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Unit tests

[codecov-io]

Codecov Report

Merging #85 into develop will increase coverage by 0.1%. The diff coverage is 83.58%.

@@            Coverage Diff             @@
##           develop      #85     +/-   ##
==========================================
+ Coverage    82.11%   82.21%   +0.1%     
==========================================
  Files           56       59      +3     
  Lines         1599     1631     +32     
  Branches        63       79     +16     
==========================================
+ Hits          1313     1341     +28     
- Misses         286      290      +4

Impacted Files	Coverage Δ
...data/waimak/dataflow/spark/SparkInterceptors.scala	100% <ø> (ø)	:arrow_up:
...a/waimak/dataflow/spark/ParquetDataCommitter.scala	98.24% <100%> (-0.09%)	:arrow_down:
...cala/com/coxautodata/waimak/dataflow/package.scala	100% <100%> (ø)	:arrow_up:
...autodata/waimak/dataflow/spark/SparkDataFlow.scala	87.32% <100%> (ø)	:arrow_up:
...ala/com/coxautodata/waimak/dataflow/DataFlow.scala	96.22% <100%> (+0.63%)	:arrow_up:
...om/coxautodata/waimak/dataflow/spark/package.scala	66.66% <66.66%> (ø)
...taflow/spark/CacheAsParquetMetadataExtension.scala	89.47% <89.47%> (ø)
...ata/waimak/dataflow/spark/SparkActionHelpers.scala	92.59% <92.59%> (ø)
...data/waimak/dataflow/CommitMetadataExtension.scala	94.87% <94.87%> (ø)
...todata/waimak/dataflow/PostActionInterceptor.scala	85.71% <0%> (-14.29%)	:arrow_down:
... and 5 more

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