feat: Warn when OIDC build feature is missing or misconfigured

[matt-richardson]

Background

When an OIDC connection's build feature is absent or misconfigured, %jwt.token% (or the connector's token_variable_name) never resolves and the octopus login fails at runtime with no easy diagnosis.

These warnings surface the misconfiguration while editing.

Results

Adds two advisory warnings to a build step's edit form, shown when the selected Octopus connection authenticates with OIDC but the build configuration lacks a correctly-configured OIDC Identity Token build feature (oidc-plugin, from teamcity-oidc-plugin):

• Feature missing — the connection uses OIDC but no oidc-plugin build feature references its connector (connection_id ≠ the connection's octopus_oidc_connection_id).
• Token variable mismatch — a matching feature exists but publishes its token under a different variable name than Octopus reads, so %<var>% never resolves.

Notes:

• The warnings do not block a save.
• Non-OIDC and no-connection steps are unaffected; when the SBuildType can't be resolved, no warning is shown.
• Inline oidc-plugin features (no connection_id) are not a supported Octopus OIDC path, so warning in that case is intended.

Screenshots

[APErebus]

Looks good to me 👍