Add prefect token var to CI when needed

[viniciusdc]

Fixes | Closes | Resolves #878

Changes introduced in this PR:

• Add a secret key to CI/CD config on GH, for when Prefect token is required
• Changed Prefect token env var syntax from TF_VAR_prefect_token to QHUB_SECRET_PREFECT_TOKEN

The reason why I changed the syntax lies in the fact we now support the direct inclusion of variables to terraform which was not feasible by Terraform infrastructure only in 0.3.+. Also, by using the QHUB_SECRET prefix, we are indeed using the omitting sensitive values settings from this type of information.

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
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Testing

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Documentation

Does your contribution include breaking changes or deprecations?
If so have you updated the documentation?

• Yes, docstrings
• Yes, main documentation
• Yes, deprecation notices

Further comments (optional)

This (Prefect) still needs to be fully tested to validate which configuration might need to be managed since the 0.4.0 changes took place. #1217

[viniciusdc]

This basically only updates the CI to catch the prefect token and add to workflow yaml, if prefect is enabled