Add integration spec "user commits changes"

• POC MR
• Step 1 - Remove IDE singleton store
• Step 2 - Defer IDE gql client creation
• Step 3 - Setup testURL in jest jsdom
• Step 4 - Setup mock server for IDE integration spec
• Step 5 - Add integration spec "user commits changes"

What does this MR do?

Adds an FE integration spec for user commits changes in the Web IDE.

Next up!

Documentation which also includes a link to this demo video 👇

References

• "Writing Frontend Integration Specs with MirageJS Environment" - the test in this MR was written in this recording.
• Related to #254254 (closed)