docs: Add Styra OPA ASP.NET Core SDK integration.

[philipaconrad]

What are the changes in this PR?

This PR adds a new OPA integration: the Styra ASP.NET Core SDK library.

Please let me know if there's any issues with the PR, and I'll patch it accordingly! 🙂

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[ashutosh-narkar]

@philipaconrad can you please look into the test failure. Thanks.

[johanfylling]

Looks like a corresponding logo file in docs/website/static/img/logos/integrations is required, as per the PR checks:

[
  {
    "key": "integration_image",
    "message": "/integrations/opa-aspnetcore/ missing image in 'static/img/logos/integrations' with extension of: png,svg"
  }
]

[philipaconrad]

Sorry for the delayed response, @ashutosh-narkar! I've pushed up a logo, so hopefully the check will pass this time around.