Install pgserver only when `pip install khoj[local]' is enabled

This avoids installing pgserver on linux arm64 docker builds, which it
doesn't currently support and isn't required to support as Khoj docker
images can use standard postgres server made available via our
docker-compose.yml

pyproject.toml

@@ -70,7 +70,6 @@ dependencies = [
     "itsdangerous == 2.1.2",
     "httpx == 0.28.1",
     "pgvector == 0.2.4",
-    "pgserver == 0.1.4",
     "psycopg2-binary == 2.9.9",
     "lxml == 4.9.3",
     "tzdata == 2023.3",
@@ -113,8 +112,11 @@ prod = [
     "twilio == 8.11",
     "boto3 >= 1.34.57",
 ]
+local = [
+    "pgserver == 0.1.4",
+]
 dev = [
-    "khoj[prod]",
+    "khoj[prod,local]",
     "pytest >= 7.1.2",
     "pytest-xdist[psutil]",
     "pytest-django == 4.5.2",