Fix E2E rules - Build GDK only on code changes

What does this MR do and why?

!117622 (diffs) accidentally added a build job to all MRs. This fixes that.

• Build the E2E GDK image under most of the same conditions as when the E2E GDK tests run. I.e., code changes, not docs.
• Rearranges some rules so that the e2e GDK tests run automatically again

MR acceptance checklist

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