Add not null constraint for file to ci_pipeline_artifacts

Ref: #234040 (closed)

What does this MR do?

This MR adds a not null contraint to our new model introduced in !37969 (merged).

Why are doing this?

We should not allow NULL in the file column in the ci_pipeline_artifacts table because it is a required field for identifying the file location.

Database Review

Note: This is a brand new table which does not contain any data.

I don't think we need to add this new constraint in multiple releases as explained in our documentation.

Please tell me if I'm wrong 🙏

Migration output

$ bin/rails db:migrate
== 20200810160355 AddNotNullConstraintToCiPipelineArtifactFile: migrating =====
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE ci_pipeline_artifacts\nADD CONSTRAINT check_abeeb71caf\nCHECK ( file IS NOT NULL )\nNOT VALID;\n")
   -> 0.0010s
-- execute("ALTER TABLE ci_pipeline_artifacts VALIDATE CONSTRAINT check_abeeb71caf;")
   -> 0.0008s
== 20200810160355 AddNotNullConstraintToCiPipelineArtifactFile: migrated (0.0158s)

Migration Rollback

$ bin/rails db:rollback
== 20200810160355 AddFNotNullConstraintToCiPipelineArtifactFile: reverting ====
-- execute("ALTER TABLE ci_pipeline_artifacts\nDROP CONSTRAINT IF EXISTS check_abeeb71caf\n")
   -> 0.0008s
== 20200810160355 AddFNotNullConstraintToCiPipelineArtifactFile: reverted (0.0063s)

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