Optional pydantic (#736)

Converts pydantic to being optional, as it is required for Airflow 2.6
but not others.

Closes #725 
Closes #654

pyproject.toml

@@ -34,10 +34,8 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
 ]
 dependencies = [
-    # Airflow & Pydantic issue: https://github.com/apache/airflow/issues/32311
     "aenum",
     "attrs",
-    "pydantic>=1.10.0,<2.0.0",
     "apache-airflow>=2.3.0",
     "importlib-metadata; python_version < '3.8'",
     "Jinja2>=3.0.0",
@@ -119,6 +117,9 @@ docker = [
 kubernetes = [
     "apache-airflow-providers-cncf-kubernetes>=5.1.1",
 ]
+pydantic = [
+        "pydantic>=1.10.0,<2.0.0",
+]
 
 
 [project.entry-points.cosmos]
@@ -164,6 +165,7 @@ matrix.airflow.dependencies = [
     { value = "apache-airflow==2.4", if = ["2.4"] },
     { value = "apache-airflow==2.5", if = ["2.5"] },
     { value = "apache-airflow==2.6", if = ["2.6"] },
+    { value = "pydantic>=1.10.0,<2.0.0", if = ["2.6"]},
     { value = "apache-airflow==2.7", if = ["2.7"] },
 ]