Align postgres hatch environment config with Snowflake

Due to an incompatibility between dbt-snowflake 1.5 and 1.6, we
had to specify the version.

Given that versioning was necessary, the benefit of using pre-install
was limited. As such, we make the relevant adapters environment-specific
dependencies, and bring postgres in line. This will hopefully get
streamlined into the bundle package in the future, but for now
we can put up with manual version management on these adapter environments.

pyproject.toml

@@ -81,6 +81,10 @@ dev-packages = [
   "types-python-dateutil",
 ]
 
+dbt-postgres = [
+  "dbt-postgres>=1.6.0.b6",
+]
+
 dbt-snowflake = [
   "dbt-snowflake>=1.6.0b3",
 ]
@@ -110,17 +114,9 @@ features = [
 
 [tool.hatch.envs.postgres-env]
 description = "Dev environment for working with Postgres adapter"
-# Install the dbt postgres package as a pre-install extra
-# This helps us avoid having to do version pegs, although it relies on pip's
-# current "pretend version conflicts aren't a problem" behavior for existing
-# installations. In future, this will be updated to use an editable dependency
-# on the dbt-metricflow bundle, which will allow for local version management
-# for testing.
-pre-install-commands = [
-  "pip install dbt-postgres",
-]
 features = [
   "dev-packages",
+  "dbt-postgres",
 ]
 
 [tool.hatch.envs.snowflake-env.env-vars]