[Bug]: Address top 404s (2025-06-05)

Top 404s for the past few weeks:

404 path | Access count | Fix
-- | -- | --
/docs/2.6/operator/ | 147 | #933[^1]
/docs/2.6/client-libraries/ | 32 | #933
/docs/2.6/opentelemetry/ | 28 | #933
/docs/2.5/client-libraries/ | 13
/docs/2.6/cli/ | 12 | #933
/docs/1.69/opentelemetry/ | 9 | #933
/docs/1.69/kubernetes/ | 5
/docs/1.69/configuration/ | 4
/docs/1.69/client-libraries/ | 3
/docs/1.8/getting-started/) | 3
/img/trace-detail.png | 3
/docs/1.27/storage/ | 2
/docs/1.27/storage/cassandra/ | 2
/docs/1.69/client-libraries | 2
/docs/1.69/elasticsearch/ | 2
/docs/2.0.6/cli/ | 2
/docs/2.0/cli/ | 2

[^1]: PR #933 doesn't directly add a rule for the path of this 404, instead it remaps e.g. `docs/operator` to an appropriate target (`/docs/1.69/operator/`) -- of which `/docs/2.6/operator/` was not.

### Steps to reproduce

Data from the GA report on 404s.

### Expected behavior

Redirect, when possible.

Start by reviewing the redirect approach described in PR #933 and compare it with the remaining paths in this issue. Check each listed 404 against the documentation site's existing redirect rules, then verify that redirects are added where an appropriate target exists and the reported paths no longer return 404.

Written by the indexing model from the issue text.