chore: remove plugins.samplestore orchestrator package

[michael-johnston]

Is your feature request related to a problem? Please describe.

Although we should support samplestore plugins we don't need the code in orchestrator/plugins/samplestore. This code is just wrapper around CSVSampleStore for parsing to particular CSV formats and there's little point in maintaining them as part of code-base.

Describe the solution you'd like.

1. Remove plugins package and subdirectories from orchestrator
2. Update tests using GT4SDTransformer or HOPV sample stores (for copying data from files with those formats to SQLSampleStore) to use CSVSampleStore
3. Update docs/examples where required

Describe alternatives you've considered.

Implementing plugin capability for sample stores and moving these files under plugins dir as samplestore plugin packages.

However these modules don't warrant being plugins.