Support .gitlab-ci.yml static validation in projects in sub-groups

What does this MR do?

Use project path and project namespace separately

This change fixes an issue when loading CI schemas in project that belong to subgroups by obtaining the namespace from the project path separately and providing it to each different components independently.

Note: This change requires the flags ci_pipeline_editor_page and schema_config to be enabled.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• 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
• Security reports checked/validated by a reviewer from the AppSec team

Related to #296519 (closed)