Declarative configuration documentation

[jaydeluca]

As part of the metadata system, we currently document system properties. We need to now implement a similar system for the new declarative configuration options.

Work to be done:

• Come up with a new format for displaying this information within the context of the metadata
• Identify if there is a way to automate the identification of these new configuration options
• Go through and update all instrumentations to document the associated configs

---

For example, the R2DBC library has:

configurations:
  - name: otel.instrumentation.r2dbc.statement-sanitizer.enabled
    description: >
      Enables statement sanitization for database queries. Takes precedence over
      otel.instrumentation.common.db-statement-sanitizer.enabled.
    type: boolean
    default: true
  - name: otel.instrumentation.common.db-statement-sanitizer.enabled
    description: Enables statement sanitization for database queries.
    type: boolean
    default: true
  - name: otel.instrumentation.r2dbc.experimental.sqlcommenter.enabled
    description: >
      Enables augmenting queries with a comment containing the tracing information. See
      [sqlcommenter](https://google.github.io/sqlcommenter/) for more info. WARNING: augmenting
      queries with tracing context will make query texts unique, which may have adverse impact on
      database performance.
    type: boolean
    default: false
  - name: otel.instrumentation.common.peer-service-mapping
    description: Used to specify a mapping from host names or IP addresses to peer services.
    type: map
    default: ""

Which could have an output like:

r2dbc:
  statement_sanitizer:
    enabled: false
  sqlcommenter/development:
    enabled: false

but unclear how we could document the description and type in this format.

Alternatively we could document them similar to how they are now, and collapsing the names:

declarative_configurations:
  - name: r2dbc.statement_sanitizer.enabled
    description: >
      Enables statement sanitization for database queries.
    type: boolean
    default: true
  - name: r2dbc.experimental.sqlcommenter/development.enabled
    description: >
      Enables augmenting queries with a comment containing the tracing information. See
      [sqlcommenter](https://google.github.io/sqlcommenter/) for more info. WARNING: augmenting
      queries with tracing context will make query texts unique, which may have adverse impact on
      database performance.
    type: boolean
    default: false

While this isn't great in the sense of being able to copy/paste it into a config, we could use it to generate a different format that is more copy/paste friendly

[jaydeluca]

Related to #15722 and #15692