Octue

Summary
Ensure bullet points render in docs. The problem may have been one of the things listed in [here](https://stackoverflow.com/questions/67542699/readthedocs-sphinx-not-rendering-bullet-list-from-rst-file). Note that some Chromium-based browsers still aren't rendering the bullet points, but Safari now is.

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Fixes
- [x] Explicitly add `sphinx-tabs` and `sphinx-rtd-theme` to `sphinx` extensions in `conf.py`

Dependencies
- [x] Use latest `sphinx-rtd-theme` for docs

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Summary
Clarify the interface for serialising `Serialisable` instances. Serialising now clearly means converting instances to a string, while a new `to_primitive` method converts instances to a dictionary of python primitives.

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Refactoring
- [x] Only allow `Serialisable.serialise` to serialise to strings
- [x] Factor new `Serialisable.to_primitive` method out from `Serialisable.serialise` and use it to replace previous usages of `Serialisable.serialise(to_string=False)`

Operations
- [x] Allow `test` branch prefix and remove the old `release` prefix

Testing
- [x] Test datafiles with spaces in name work as expected

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Enhancements
- [x] Let `FilterContainer.one` be used with no filters on empty containers

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Fixes
- [x] Upload dataset metadata file for cloud directory datasets when getting a dataset from a cloud directory with no existing metadata file

Refactoring
- [x] Rename `dataset.json file` to `dataset_metadata.json`
- [x] Simplify `Dataset.from_cloud`

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Operations
- [x] Update pull request workflow

Refactoring
- [x] Use more resilient method to list blobs in a cloud directory

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Fixes
- [x] Allow `Manifest` construction from any serialized cloud dataset

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