Code Graph: re-index when we bump the version of an indexer

[olafurpg]

Currently, when we bump up the version of an indexer then we still keep old indexes with the old version. Keeping old indexes can cause problems when the new version fixes a critical bug. The issue sourcegraph/scip-typescript#247 is one example where we thought scip-typescript had a bug but the issue was that sourcegraph.com was identifying the definition of a symbol from an old version of scip-typescript. When I manually deleted the index on sourcegraph.com then the navigation became correct.

Slack discussion https://sourcegraph.slack.com/archives/CHXHX7XAS/p1681327195530239

This issue is a feature request to automatically mark indexes as re-indexable when the version differs from the version/tag we supply to the inference engine.