Move default CSP initialization out of 1_settings.rb

What does this MR do?

Fixes #338361 (closed)

To generate the most useful content-security-policy possible, some GitLab settings are read on initialization. Because we were reading settings that hadn't been initialized yet there was an error on application startup.

The CSP directives default values are now generated only if needed outside of the 1_settings.rb file so we don't depend on the order of initialization of settings anymore.

The bug was introduced in !67791 (merged) and didn't have the time to make it into a release.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Make sure that the sentry settings are not defined in gitlab.yml and start the application. This used to crash before the changes in this MR.

Does this MR meet the acceptance criteria?

Conformity

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• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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