Previously, Sourcegraph Enterprise instances with context filters
enabled rejected requests from all unknown clients out of concern that
they might not respect context filters. This behavior makes it
incredibly impractical to release now agent-based clients (CLI, Eclipse,
Visual Studio, Neovim, ..) that do respect context filters out of
the box thanks to the reused logic in the Cody agent.

This logic suffers from both false positives and false negatives:

- False negatives: upcoming Cody clients (CLI, Eclipse, Visual Studio)
  already support context filters out of the box thanks to using the
  Cody agent but they can't send requests unless we add a special case
  to them.
- False positive: a malicious client can always fake that it's
  "jetbrains" with a valid version number even if the client doesn't
  respect context filters. This gives a false sense of security because
  it doesn't prevent malicious traffic from bypassing context filters.

Now, with this change, Sourcegraph Enterprise instances only reject
requests from old versions of Cody clients that are known to not support
context filters. This ensures we never have false positives or false
negatives.