feat(gateway): Oauth2 token support in event plugins

[lena-larionova]

Description

Adds auth tables and examples.
No how-to guide at the moment; might add one in the future for one of the plugins (a separate one for each would be overkill).

Fixes #5404
Fixes #5405

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[Copilot]

Pull request overview

This PR updates several Event Gateway-related plugin docs (Solace, Kafka, and Confluent) to document OAuth2 token-based authentication support, adding shared “Authentication” sections and new plugin configuration examples (OAuth2 client credentials / SASL OAUTHBEARER) targeting {{site.base_gateway}} 3.15.

Changes:

• Adds shared authentication tables (auth.md includes) and wires them into affected plugin overview pages.
• Introduces new OAuth2-focused plugin examples for Solace (client credentials) and Kafka/Confluent (SASL/OAUTHBEARER).
• Updates one existing include invocation formatting in Solace Log to avoid malformed Liquid/Markdown rendering.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
app/_kong_plugins/solace-upstream/index.md	Adds an Authentication section referencing the shared Solace auth include.
app/_kong_plugins/solace-upstream/examples/oauth-client-credentials.yaml	Adds a new Solace OAuth2 client credentials example (Gateway 3.15+).
app/_kong_plugins/solace-log/index.md	Fixes include formatting and adds an Authentication section for Solace Log.
app/_kong_plugins/solace-log/examples/oauth-client-credentials.yaml	Adds a new Solace Log OAuth2 client credentials example (Gateway 3.15+).
app/_kong_plugins/solace-consume/index.md	Adds an OAuth2 example entry and an Authentication section for Solace Consume.
app/_kong_plugins/solace-consume/examples/oauth-client-credentials.yaml	Adds a new Solace Consume OAuth2 client credentials example (Gateway 3.15+).
app/_kong_plugins/kafka-upstream/index.md	Adds an Authentication section referencing the shared Kafka auth include.
app/_kong_plugins/kafka-upstream/examples/oauthbearer.yaml	Adds a new Kafka Upstream SASL/OAUTHBEARER example (Gateway 3.15+).
app/_kong_plugins/kafka-log/index.md	Adds an Authentication section referencing the shared Kafka auth include.
app/_kong_plugins/kafka-log/examples/oauthbearer.yaml	Adds a new Kafka Log SASL/OAUTHBEARER example (Gateway 3.15+).
app/_kong_plugins/kafka-consume/index.md	Adds an Authentication section referencing the shared Kafka auth include.
app/_kong_plugins/kafka-consume/examples/oauthbearer.yaml	Adds a new Kafka Consume SASL/OAUTHBEARER example (Gateway 3.15+).
app/_kong_plugins/confluent/index.md	Adds an Authentication section referencing the shared Confluent auth include.
app/_kong_plugins/confluent/examples/oauthbearer.yaml	Adds a new Confluent SASL/OAUTHBEARER example (Gateway 3.15+).
app/_kong_plugins/confluent-consume/index.md	Adds an Authentication section referencing the shared Confluent auth include.
app/_kong_plugins/confluent-consume/examples/oauthbearer.yaml	Adds a new Confluent Consume SASL/OAUTHBEARER example (Gateway 3.15+).
app/_includes/plugins/solace/auth.md	New shared Solace authentication schemes table and example links per plugin.
app/_includes/plugins/kafka/auth.md	New shared Kafka SASL mechanism table and example links per plugin.
app/_includes/plugins/confluent/auth.md	New shared Confluent Cloud authentication options table and example link.