feat: add option to define the Sentry Environment

What does this MR do?

Error Reporting and Logging with Sentry is supported for several components, this MR provides the option to define the Sentry Environment within the application settings.

This is especially useful to track errors and issues across several deployed GitLab environments, e.g. lab, dev, stage, prod. With this MR Issues for all environments can be tracked within one Sentry project. The feature has been addressed within #49771 (closed)

UPDATE

This MR was initially based on adding addition application settings for the client and server side Sentry settings. During the discussion we agreed on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27091#note_158941995 . So this MR shall do the following:

1. Add Gitlab.config.sentry.enabled, Gitlab.config.sentry.dsn and Gitlab.config.sentry.environment options within config/gitlab.yml;
2. Fallback the Sentry settings on "Error Reporting and Logging" section to the values on config/gitlab.yml if they are not set;
3. Add a deprecation warning on "Error Reporting and Logging" section;
4. Add a deprecation warning on the release post;
5. Update documentation;

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [ ] Separation of EE specific content not applicable