API docs: default search indexing to off temporarily

Created by: slimsag

Once search indexing finished, CPU usage of codeintel-db spiked up due to an issue with the OOB migration #25856 (closed) and I have now identified some more key schema changes we'll need to make to have this table scale better.

Defaulting search indexing to off for now and will re-enable by default once I've made some of these key changes.

Signed-off-by: Stephen Gutekanst stephen@sourcegraph.com