OpenTelemetry collector mode

.changesets/add-collector-attribute-options.md

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+---
+bump: minor
+type: add
+---
+
+Add configuration options that map to OpenTelemetry resource attributes in collector mode: `service_name`, `filter_attributes`, `filter_function_parameters`, `filter_request_query_parameters`, `filter_request_payload`, `response_headers`, `send_function_parameters`, `send_request_query_parameters` and `send_request_payload`.
+
+In collector mode, existing options are passed to the collector as resource attributes as well: `name`, environment, `hostname`, `revision`, `ignore_actions`, `ignore_errors`, `ignore_namespaces`, `request_headers`, `filter_session_data` and `send_session_data`.
+
+Setting any of these without `collector_endpoint`, or setting `filter_parameters`, `filter_metadata` or `send_params` with it, logs a warning at startup.

.changesets/add-collector-mode.md

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+---
+bump: major
+type: add
+---
+
+Add a `collector_endpoint` configuration option (`APPSIGNAL_COLLECTOR_ENDPOINT` environment variable) that puts the integration in _collector mode_. In collector mode AppSignal reports traces, metrics and logs to an AppSignal Collector, over OTLP/HTTP.
+
+Collector mode requires Ruby 3.1 or newer, and the OpenTelemetry gems, which are not installed by default. Add the `appsignal-opentelemetry` gem alongside `appsignal` to install them. When they are missing or too old, AppSignal logs a warning and keeps reporting through its agent.