main: postgres is now an optional dependency

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "carte-cli"
-version = "0.2.1"
+version = "0.2.2"
 description = "A static site generator for data catalogs"
 authors = ["Balint Haller <balint@hey.com>"]
 license = "Apache-2.0"
@@ -19,8 +19,11 @@ amundsen-databuilder = "^4.1.0"
 boto3 = "^1.17.2"
 typer = "^0.3.2"
 click-spinner = "^0.1.10"
-SQLAlchemy = "^1.3.23"
-psycopg2 = "^2.8.6"
+psycopg2 = { version = "^2.8.6", optional = true }
+SQLAlchemy = { version = "^1.3.23", optional = true }
+
+[tool.poetry.extras]
+postgres = ["psycopg2", "SQLAlchemy"]
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]