BE: Add embargo to unique fields

[tushortz]

Description

This PR includes the following:

• Add embargo field to APITimeSeries unique constraint
• Add embargo field to CoreTimeSeries unique constraint
• Add embargo field to CoreHeadline unique constraint

Fixes #CDD-2977

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Type of change

Please select the options that are relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Tech debt item (this is focused solely on addressing any relevant technical debt)

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Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests at the right levels to prove my change is effective
• I have added screenshots or screen grabs where appropriate
• I have added docstrings in the correct style (google)

[aidan]

@tushortz I think you need to turn off autosort imports and check the migrations that are being generated?

Done

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud