feat: issue estimations (#696)

* dev: initialize estimation

* dev: issue estimation field in issues and project settings

* dev: update issue estimation logic

apiserver/plane/api/serializers/estimate.py

@@ -0,0 +1,25 @@
+# Module imports
+from .base import BaseSerializer
+
+from plane.db.models import Estimate, EstimatePoint
+
+
+class EstimateSerializer(BaseSerializer):
+    class Meta:
+        model = Estimate
+        fields = "__all__"
+        read_only_fields = [
+            "workspace",
+            "project",
+        ]
+
+
+class EstimatePointSerializer(BaseSerializer):
+    class Meta:
+        model = EstimatePoint
+        fields = "__all__"
+        read_only_fields = [
+            "estimate",
+            "workspace",
+            "project",
+        ]