Refactor database configuration for flexibility

Introduced a .env file to store the DATABASE_URL, enhancing configuration management. Updated GitHub Actions workflow and example schema to use the environment variable. This change centralizes the database configuration and improves maintainability.

.env

@@ -0,0 +1 @@
+DATABASE_URL=postgres://example:example@localhost:5432/example

.github/workflows/crystal.yml

@@ -53,6 +53,8 @@ jobs:
       - name: Check code style
         run: crystal tool format --check
       - name: Run tests
+        env:
+          DATABASE_URL: postgres://example:example@localhost:5432/example
         run: crystal spec
 
   docs:

spec/schemas/example.cr

@@ -3,7 +3,7 @@ require "pg"
 Example = Cql::Schema.build(
   :example,
   adapter: Cql::Adapter::Postgres,
-  uri: "postgres://example:example@localhost:5432/example") do
+  uri: ENV["DATABASE_URL"]) do
   table :customers, as: "cust" do
     primary :customer_id, Int64, auto_increment: true
     column :customer_name, String, as: "cust_name"