Setup mock server for IDE integration spec (RUN AS-IF-FOSS)

• 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?

This MR sets up the initial mock server for IDE integration spec.

Screenshots

Video explaining how to use the mock server in development to write integration specs is coming!

References

• Related to #208800 (closed)