chore: tighten datadog pin and move it to requirements-base (#15823)

requirements-base.txt

@@ -8,6 +8,7 @@ confluent-kafka==0.11.5
 # 'cryptography>=1.3,<1.4
 croniter>=0.3.26,<0.4.0
 cssutils==1.0.2
+datadog>=0.15.0,<0.31.0
 django-crispy-forms==1.6.1
 django-picklefield>=0.3.0,<1.1.0
 django-sudo>=2.1.0,<3.0.0

requirements-dev.txt

@@ -1,5 +1,4 @@
 Babel
-datadog
 docker>=3.7.0,<3.8.0
 exam>=0.5.1
 freezegun==0.3.11