docs: update default value for trace api configurations [backport 1.20] (#7205)

Backport 9fd054c from #7199 to 1.20.

Follows up: #6947

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Co-authored-by: Munir Abdinur <[email protected]>

Author: github-actions[bot]

docs/configuration.rst

@@ -280,14 +280,15 @@ The following environment variables for the tracer are supported:
 
    DD_TRACE_API_VERSION:
      default: |
-         ``v0.5`` if priority sampling is enabled, else ``v0.3``
+         ``v0.4``
      description: |
          The trace API version to use when sending traces to the Datadog agent.
 
          Currently, the supported versions are: ``v0.3``, ``v0.4`` and ``v0.5``.
      version_added:
        v0.56.0:
        v1.7.0: default changed to ``v0.5``.
+       v1.19.1: default reverted to ``v0.4``.
 
    DD_TRACE_OBFUSCATION_QUERY_STRING_REGEXP:
      default: |