Add Content-Security-Policy header to nginx config

[VladyslavTy]

We need to provide access for the specified hosts to show the Tahoe website as iframe. To handle this we need to add new header into the Nginx configurations add_header Content-Security-Policy "frame-ancestors www.test.com". The value will take from the edx-config environments and placed into the configurations while deploying process.
This is a part of the ENG-714 that is related to Seertech IDP integration we make for Snowflake.

Make sure that the following steps are done before merging:

• A DevOps team member has approved the PR if it is code shared across multiple services and you don't own all of the services.
• Are you adding any new default values that need to be overridden when this change goes live? If so:
  • Update the appropriate internal repo (be sure to update for all our environments)
  • If you are updating a secure value rather than an internal one, file a DEVOPS ticket with details.
  • Add an entry to the CHANGELOG.
• If you are making a complicated change, have you performed the proper testing specified on the Ops Ansible Testing Checklist? Adding a new variable does not require the full list (although testing on a sandbox is a great idea to ensure it links with your downstream code changes).
• Think about how this change will affect Open edX operators. Have you updated the wiki page for the next Open edX release?

[VladyslavTy]

Going to merge without passing the tests as it have no changes to the existing codebase, but only adding new value.