Add metrics_prefix to discovery block (DataDog#24861)

* Manually author discovery metrics_prefix in spec.yaml for gearmand, krakend, prefect

Alternative to PR DataDog#24738's auto-detection approach, which computed each
integration's metrics_prefix from manifest.json or the repo's
.ddev/config.toml override table at `ddev validate config` time. Integration
owners raised a concern that this made .ddev/config.toml, a developer/tooling
config file, silently production-critical, since a wrong or missing entry
there would flow straight into the auto_conf.yaml shipped with the Agent.

This hand-authors the same metrics_prefix values directly in each
integration's assets/configuration/spec.yaml via a discovery.example override
on the existing auto_conf/discovery template, using the same override
mechanism already used for ad_identifiers' value.example and krakend's
cel_selector.example. auto_conf.yaml is then regenerated with `ddev validate
config -s`, producing output identical to PR DataDog#24738's.

Environment: Datadog workspace

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* Add changelog entries for PR DataDog#24861

Environment: Datadog workspace

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: vitkyrka

gearmand/assets/configuration/spec.yaml

@@ -55,3 +55,6 @@ files:
       value.example:
       - gearmand
   - template: auto_conf/discovery
+    overrides:
+      discovery.example:
+        metrics_prefix: gearman

gearmand/changelog.d/24861.added

@@ -0,0 +1 @@
+Add ``metrics_prefix`` to the ``discovery`` block of ``auto_conf.yaml``.

gearmand/datadog_checks/gearmand/data/auto_conf.yaml

@@ -8,7 +8,8 @@ ad_identifiers:
 
 ## Enables configuration discovery
 #
-discovery: {}
+discovery:
+  metrics_prefix: gearman
 
 ## Unused init configuration
 #

krakend/assets/configuration/spec.yaml

@@ -86,3 +86,6 @@ files:
         processes:
           - "process.name == 'krakend'"
   - template: auto_conf/discovery
+    overrides:
+      discovery.example:
+        metrics_prefix: krakend.api

krakend/changelog.d/24861.added

@@ -0,0 +1 @@
+Add ``metrics_prefix`` to the ``discovery`` block of ``auto_conf.yaml``.

krakend/datadog_checks/krakend/data/auto_conf.yaml

@@ -14,7 +14,8 @@ cel_selector:
 
 ## Enables configuration discovery
 #
-discovery: {}
+discovery:
+  metrics_prefix: krakend.api
 
 ## Unused init configuration
 #

prefect/assets/configuration/spec.yaml

@@ -160,4 +160,7 @@ files:
       value.example:
       - prefect
   - template: auto_conf/discovery
+    overrides:
+      discovery.example:
+        metrics_prefix: prefect.server
 

prefect/changelog.d/24861.added

@@ -0,0 +1 @@
+Add ``metrics_prefix`` to the ``discovery`` block of ``auto_conf.yaml``.

prefect/datadog_checks/prefect/data/auto_conf.yaml

@@ -8,7 +8,8 @@ ad_identifiers:
 
 ## Enables configuration discovery
 #
-discovery: {}
+discovery:
+  metrics_prefix: prefect.server
 
 ## Unused init configuration
 #