Twined

Summary
Remove the credentials environment variable name from the children schema. The default `GOOGLE_APPLICATION_CREDENTIALS` is the only name now used in `octue-sdk-python`.

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Contents ([98](https://github.com/octue/twined/pull/98))

Enhancements
- Remove the credentials environment variable name from the children schema
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Summary
Simplify specification of datasets in twines and manifests.

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Contents ([95](https://github.com/octue/twined/pull/95))
**IMPORTANT:** There are 2 breaking changes.

Enhancements
- **BREAKING CHANGE:** Require "datasets" field to be a dictionary in `manifest.json` files
- **BREAKING CHANGE:** Require "datasets" field in the "manifest" strands of `twine.json` to be a dictionary
- Raise error if JSON objects contain duplicate keys

Fixes
- Use correct method to transform manifests during validation
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Because we ran out of free credit on Travis!

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Contents ([94](https://github.com/octue/twined/pull/94))

Operations
- Skip pull request description update if skip indicator in body

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Contents ([93](https://github.com/octue/twined/pull/93))

Operations
- Add and apply `pydocstyle` docstring linting to `pre-commit`
- Add and apply `pep8-naming` `flake8` extension to `pre-commit`

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Contents ([92](https://github.com/octue/twined/pull/92))

New features
- Add ability to validate monitor updates

Operations
- Use latest conventional commits pre-commit version

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Quality Checklist
- [x] New features are fully tested