Web IDE show alert when project rejects unsigned commits

• Expose project.pushRules in gql
• Web IDE show alert when project rejects unsigned commits

What does this MR do?

See relevant comment for context.

This MR updates the Web IDE to disable the commit button and show an alert when a project has the "reject unsigned commits" push rule checked.

Screenshots (strongly suggested)

IDE (with rejectUnsignedCommits: true)	IDE disabled tooltip (with rejectUnsignedCommits: true)	IDE (with rejectUnsignedCommits: true) but no license

• Note that no alert is shown when there is no license, because this is a Premium feature.

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

References

• Related to #213581 (closed)