Adding Key Value Pairs from logback to Splunk automatically.

[djpimienta]

Hey Y'all,
I'm sure I'm missing something but I'm not sure I've got the right context to figure it out. Recently, our organization switched to using the otel-collector and splunk to display our logs.
We have some context that we include by adding to them to ILoggingEvents

which we could configure to be picked up by the logger:
%kvp{NONE}%n<>snip
and this all still works with our added properties being picked up by the logger and this was enough to have
Then we added the otel appender:

    <appender name="OpenTelemetry" class="com.proofpoint.logback.appender.OtlpHttpAppender">
        <url>http://splunk-otel-collector-${AVAILABILITY_ZONE_LETTER}.monitoring.svc.cluster.local:4318/v1/logs</url>
        <customFields>{"fl_name":"${SERVICE_NAME}","service_version":"${SERVICE_VERSION}","fake_field":"FakeInfo"}</customFields>
        <captureMdcAttributes>*</captureMdcAttributes>
        <captureKeyValuePairAttributes>*</captureKeyValuePairAttributes>
        <captureLoggerContext>*</captureLoggerContext>
        <appender-ref ref="stdout" />
    </appender>
    <root level="${LOGLEVEL_DEFAULT:-INFO}">
        <appender-ref ref="stdout" />
        <appender-ref ref="async-console" />
        <appender-ref ref="OpenTelemetry" />
    </root>

Our Dev Ops has an otel collector running with the following config for adding attributes which works:

"transform/add_attributes" = {
              "log_statements" = [
                {
                  "context" = "log"
                  "statements" = [
                    # Set the environment name for all logs
                    "set(attributes[\"environment\"], \"${local.environment}\")",
                    # Copy the logback severity if it exists into the log_level attribute
                    "set(attributes[\"log_level\"], severity_text)",
                    # Move expected attributes from logback MDC
                    "set(attributes[\"fl_name\"], attributes[\"logback.mdc.fl_name\"])",
                    "delete_key(attributes, \"logback.mdc.fl_name\")",
                    "set(attributes[\"service_version\"], attributes[\"logback.mdc.service_version\"])",
                    "delete_key(attributes, \"logback.mdc.service_version\")",
                    # Set the name of the otel-collector-gateway pod name
                    "set(attributes[\"otel_collector_gateway_pod\"], \"$${K8S_POD_NAME}\")",
                    "set(attributes[\"gateway_az\"], \"${module.common_config.aws_region}${AZ}\")",
                  ]
                }
              ]
            }
            "transform/set_logs_as_json_in_body" = {
              "log_statements" = [
                {
                  "context" = "log"
                  "statements" = [
                    # Declare an empty map and then add attributes and body onto it
                    "set(cache[\"event_json\"], ParseJSON(\"{}\"))",
                    "merge_maps(cache[\"event_json\"], attributes, \"upsert\")",
                    "delete_key(cache[\"event_json\"], \"otel_collector_agent_pod\")",
                    "delete_key(cache[\"event_json\"], \"otel_collector_gateway_pod\")",
                    "delete_key(cache[\"event_json\"], \"gateway_az\")",
                    "set(cache[\"event_json\"][\"_log\"], body)",
                    # Remove the attributes that moved to the event_json
                    "keep_keys(attributes, [\"otel_collector_agent_pod\", \"otel_collector_gateway_pod\", \"gateway_az\"])",
                    # Override body with the new json
                    "set(body, cache[\"event_json\"])",
                  ]
                }
              ]
            }

We were led to believe that this would be enough to have these show up as attributes in Splunk.
However, this didn't happen and after reading the configs and documentation and I'm not sure if there is anyway to add more attributes without explicitly defining them(like 'fl_name' or 'otel_collector_gateway_pod') or in the collector config using OTEL_RESOURCE_ATTRIBUTES?

Is there a way to set attributes by looping through the json/a way to get all the added properties? Can someone point me to what I missed in the transform docs?