JetBrains: Fix hardcoded Sourceraph URLs

Created by: philipp-spiess

Fixes #38296 (closed)

There were two places that still used the hard-coded sourcegraph.com URL instead of picking one from the instanceURL config.

I also added the instanceURL as a key so that we recreate the whole search input in case it changes to avoid it using a wrong config.

Test plan

I changed the URL to k8s.sgdev.org to test if it works:

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