[DOC] Make codetheweb and rescrv co-owners of the crates we publish for the client. (#5718)

## Description of changes

To keep tabs on the client's changes, add code owners so that we can
automatically tag for review changes to the client that we ship.

## Test plan

CI

## Migration plan

N/A

## Observability plan

N/A

## Documentation Changes

N/A

Author: rescrv

.github/CODEOWNERS

@@ -0,0 +1,4 @@
+# CODEOWNERS for Rust components
+rust/error/ @codetheweb @rescrv
+rust/api_types/ @codetheweb @rescrv
+rust/chroma/ @codetheweb @rescrv