Batch executor mvp docs

Created by: malomarrec

A super MVP "fake docs page" of the end state of Batch Changes runners. Once this is complete, we can show it to customers to gather high fidelity feedback. We can iterate and prototype in parallel.

Blocking feedback session

• Add prerequisites section @LawnGnome
• Add "How do runners work" section @LawnGnome
• Add to Limitations section @LawnGnome
• Add "Runner vs CLI workflow" section @malomarrec
• Reply to FAQ @malomarrec @LawnGnome
• !!! add disclaimer and "on construction" to set expectations with customers

Then

• organise session with customers and @malomarrec @rrhyne

Not-blocking feedback session

• https://github.com/sourcegraph/sourcegraph/issues/22099