RFC 697: Testing - Delivery user story

Created by: efritz

See RFC 697: Multiple version upgrades.

This PR tracks general testing of multi-version upgrades as well as delivery-specific test scenarios.

See the testing strategy announcement in slack.

Core story:

1. Run a search for the sourcegraph/sourcegraph repository
2. Search for the term GetUploads on HEAD
3. Open a result and ensure the file renders
4. Check that file sidebar and symbols sidebars are populated
5. Ensure code navigation (go to definition and find references) work as expected
6. Repeat steps 2-5 on an old tag to ensure that unindexed paths are also functional
7. Visit each site-admin page to ensure there are no obvious error banners

Instructions:

The following issues provide detailed instructions for upgrading a single-server image distribution of Sourcegraph:

• #40702
• #40700
• #40703 (closed)
• #40704
• #40701

Similar instructions should be performed on both a docker-compose deployment and a Kubernetes deployment. There are existing docs on how to run migrator commands in a custom environment.