Include SafeQL configuration conditionally

[Karl Horky]

Only enable the SafeQL configuration if:

• If @ts-safeql/eslint-plugin and dotenv-safe are installed in the project (in combined dependencies and devDependencies in package.json)
• If the environment variables are available via dotenv-safe
• If the platform is not Windows, until the following issues are resolved:
  • ts-safeql/safeql#80
  • launchql/libpg-query-node#22
  • pganalyze/libpg_query#44

[Karl Horky]

We may be able to enable SafeQL on Windows soon:

• #297