Fix migrations + ensure functionality

Author: thelenw

server/src/main/resources/db/common/V107__create_volunteering_tables.sql

@@ -16,7 +16,7 @@ CREATE TABLE volunteering_relationship
     relationship_id varchar PRIMARY KEY,
     member_id       varchar REFERENCES member_profile (id),
     organization_id varchar REFERENCES volunteering_organization (organization_id),
-    start_date      timestamp,
+    start_date      timestamp NOT NULL,
     end_date        timestamp,
     is_active       boolean   NOT NULL DEFAULT TRUE
 );

server/src/main/resources/db/common/V115__alter_volunteering_relationship.sql

@@ -0,0 +1,2 @@
+ALTER TABLE volunteering_relationship
+ALTER COLUMN start_date DROP NOT NULL;