Add operator for resolving the epoch data path

[glopesdev]

This PR introduces a new operator for resolving the epoch data path used by RepositoryLogController. The expected behavior is reproduced in the following flowchart.

flowchart LR
    A{Is Repo\nClean?} --> |no|B
    B(Detached\nHead?) --> |no|C
    B --> |yes|D
    C[fallback/branch-sha1]
    D[fallback/detached-sha1]
    A --> |yes|E
    E{Is Commit\nTagged?} --> |no|B
    E --> |yes|F
    F[data/tagname]

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The tag name is assumed to end with a full semver string from which all characters after the last dot are removed. Changes to the tag version assume that what we are versioning is the data schema of the experiment:

• Changing the format of an existing stream or data file > change the major version
• Adding a new stream to the existing schema > change the minor version (note: schemas targeting older minor versions can still open this data)
• Removing a stream from an experiment:
  • one perspective > dataset is broken
  • other perspective > data is just empty for that stream
  • finally we could make this into a schema setting (i.e. certain streams are always required)
• Changing anything that doesn't affect the schema or data formats > change the patch version

Fixes SainsburyWellcomeCentre/aeon_experiments#291