chore(ci): update config registry with backfilled option (#304)

The backfilled option showed some issue with the current state of
the supported-configurations.json. This is fixed by this PR by
setting the backfilled option to true as well as updating the generation
script to:
- lower case types
- use true and false as boolean
- use exact decimal values as defined in the macro

The script now also preserves the former implementation used, if re-run.

In addition, change DD_TRACE_RATE_LIMIT and
DD_TELEMETRY_EXTENDED_HEARTBEAT_INTERVAL decimal types to integers.

The DD_INSTRUMENTATION_INSTALL_ID, DD_INSTRUMENTATION_INSTALL_TYPE,
DD_INSTRUMENTATION_INSTALL_TIME, and DD_EXTERNAL_ENV default values
were changed from an empty string to nullptr, since that seemed more
suitable for these configurations.

Author: BridgeAR

.gitlab-ci.yml

@@ -21,7 +21,7 @@ validate_supported_configurations_v2_local_file:
   extends: .validate_supported_configurations_v2_local_file
   variables:
     LOCAL_JSON_PATH: "supported-configurations.json"
-    BACKFILLED: false
+    BACKFILLED: true
 
 update_central_configurations_version_range_v2:
   stage: config-validation

.gitlab/config-registry.yml

@@ -19,7 +19,7 @@ variables:
     - when: on_success
   variables:
     LOCAL_JSON_PATH: ""
-    BACKFILLED: ""
+    BACKFILLED: "true"
   before_script:
     - *download-scripts-from-template
   script:

include/datadog/environment.h

@@ -35,6 +35,9 @@ namespace environment {
 //       The runtime default is resolved in C++ configuration finalization
 //       logic. The description is emitted as the "default" field in
 //       metadata/supported-configurations.json.
+//   - nullptr
+//       There is no default value. This is emitted as JSON null in
+//       metadata/supported-configurations.json.
 #define DD_LIST_ENVIRONMENT_VARIABLES(MACRO)                                   \
   MACRO(DD_AGENT_HOST, STRING, "localhost")                                    \
   MACRO(DD_ENV, STRING, "")                                                    \
@@ -60,29 +63,29 @@ namespace environment {
             "then defaults to http://localhost:8126."))                        \
   MACRO(DD_TRACE_DEBUG, BOOLEAN, false)                                        \
   MACRO(DD_TRACE_ENABLED, BOOLEAN, true)                                       \
-  MACRO(DD_TRACE_RATE_LIMIT, DECIMAL, 100.0)                                   \
+  MACRO(DD_TRACE_RATE_LIMIT, INT, 100)                                         \
   MACRO(DD_TRACE_REPORT_HOSTNAME, BOOLEAN, false)                              \
-  MACRO(DD_TRACE_SAMPLE_RATE, DECIMAL, 1.0)                                    \
+  MACRO(DD_TRACE_SAMPLE_RATE, DECIMAL, 1)                                      \
   MACRO(DD_TRACE_SAMPLING_RULES, ARRAY, "[]")                                  \
   MACRO(DD_TRACE_STARTUP_LOGS, BOOLEAN, true)                                  \
   MACRO(DD_TRACE_TAGS_PROPAGATION_MAX_LENGTH, INT, 512)                        \
   MACRO(DD_VERSION, STRING, "")                                                \
   MACRO(DD_TRACE_128_BIT_TRACEID_GENERATION_ENABLED, BOOLEAN, true)            \
   MACRO(DD_TELEMETRY_HEARTBEAT_INTERVAL, DECIMAL, 10)                          \
-  MACRO(DD_TELEMETRY_EXTENDED_HEARTBEAT_INTERVAL, DECIMAL, 86400.0)            \
+  MACRO(DD_TELEMETRY_EXTENDED_HEARTBEAT_INTERVAL, INT, 86400)                  \
   MACRO(DD_TELEMETRY_METRICS_ENABLED, BOOLEAN, true)                           \
   MACRO(DD_TELEMETRY_METRICS_INTERVAL_SECONDS, DECIMAL, 60)                    \
   MACRO(DD_TELEMETRY_DEBUG, BOOLEAN, false)                                    \
   MACRO(DD_TRACE_BAGGAGE_MAX_ITEMS, INT, 64)                                   \
   MACRO(DD_TRACE_BAGGAGE_MAX_BYTES, INT, 8192)                                 \
   MACRO(DD_TELEMETRY_LOG_COLLECTION_ENABLED, BOOLEAN, true)                    \
-  MACRO(DD_INSTRUMENTATION_INSTALL_ID, STRING, "")                             \
-  MACRO(DD_INSTRUMENTATION_INSTALL_TYPE, STRING, "")                           \
-  MACRO(DD_INSTRUMENTATION_INSTALL_TIME, STRING, "")                           \
+  MACRO(DD_INSTRUMENTATION_INSTALL_ID, STRING, nullptr)                        \
+  MACRO(DD_INSTRUMENTATION_INSTALL_TYPE, STRING, nullptr)                      \
+  MACRO(DD_INSTRUMENTATION_INSTALL_TIME, STRING, nullptr)                      \
   MACRO(DD_APM_TRACING_ENABLED, BOOLEAN, true)                                 \
   MACRO(DD_TRACE_RESOURCE_RENAMING_ENABLED, BOOLEAN, false)                    \
   MACRO(DD_TRACE_RESOURCE_RENAMING_ALWAYS_SIMPLIFIED_ENDPOINT, BOOLEAN, false) \
-  MACRO(DD_EXTERNAL_ENV, STRING, "")
+  MACRO(DD_EXTERNAL_ENV, STRING, nullptr)
 
 #define ENV_DEFAULT_RESOLVED_IN_CODE(X) X
 #define WITH_COMMA(ARG, TYPE, DEFAULT_VALUE) ARG,