feat!: implement AI Bridge heading to /deployment/observability (#20791)

> [!CAUTION]
> In whichever release this lands, we've removed the ability to provide
keys via a YAML file (specifically on `openai_key`, `anthropic_key`,
`bedrock_access_key` and finally `bedrock_access_key_secret`). This will
need to be described in the release notes as to not break peoples AI
Bridge integrations upgrading from older versions.

This pull-request ensures that we can see the overview of the settings
of the `AI Bridge` feature within the `/deployment/observability` route.
This set of options only render when the `aibridge` feature flag is
enabled.

### Preview


![preview-ai-bridge-observability](https://github.com/user-attachments/assets/262d2456-94b4-49b2-9b4e-b14583e70ede)

cli/testdata/server-config.yaml.golden

@@ -720,25 +720,12 @@ aibridge:
   # The base URL of the OpenAI API.
   # (default: https://api.openai.com/v1/, type: string)
   openai_base_url: https://api.openai.com/v1/
-  # The key to authenticate against the OpenAI API.
-  # (default: <unset>, type: string)
-  openai_key: ""
   # The base URL of the Anthropic API.
   # (default: https://api.anthropic.com/, type: string)
   anthropic_base_url: https://api.anthropic.com/
-  # The key to authenticate against the Anthropic API.
-  # (default: <unset>, type: string)
-  anthropic_key: ""
   # The AWS Bedrock API region.
   # (default: <unset>, type: string)
   bedrock_region: ""
-  # The access key to authenticate against the AWS Bedrock API.
-  # (default: <unset>, type: string)
-  bedrock_access_key: ""
-  # The access key secret to use with the access key to authenticate against the AWS
-  # Bedrock API.
-  # (default: <unset>, type: string)
-  bedrock_access_key_secret: ""
   # The model to use when making requests to the AWS Bedrock API.
   # (default: global.anthropic.claude-sonnet-4-5-20250929-v1:0, type: string)
   bedrock_model: global.anthropic.claude-sonnet-4-5-20250929-v1:0