Resolve "Pipeline Editor freezes when using include: rules:

What does this MR do and why?

Fixes a bug where the editor app would freeze when getting a 500 error from the API. We now gracefully display the error and keep the editor working.

Screenshots or screen recordings

Before	After
	Screen_Recording_2021-11-05_at_1.53.15_PM

How to set up and validate locally

1. Go to CI/CD => editor
2. Write

include:
  rules:
    -

Once this is written, the editor will crash if not on this MR branch. Now do the same thing on this branch to compare!

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #344836 (closed)