docs: Added database connection documentation

[koenmtb1]

Related issue

Issue discussed in Slack with @zepatrik. No documentation for how to connect to a database was available.

Proposed changes

Adding documentation for how to connect to a database.

Checklist

• I have read the contributing guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security.
  vulnerability, I confirm that I got green light (please contact security@ory.sh) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added or changed the documentation.

[zepatrik]

Can you add your example here? It should then be rendered into the markdown file.

Suggested change

	"description": "DSN is used to specify the database credentials as a connection URI."
	"description": "DSN is used to specify the database credentials as a connection URI.",
	"examples": ["postgres://user:password@localhost:5432/database"]

To regenerate the configuration page run (in the project's root directory)

$ node docs/scripts/config.js docs/config.js

and then commit the markdown aswell.
We should really document how to do that.

[koenmtb1]

Okay, did that. I also added a quick instruction for how to do it in the CONTRIBUTING.md. Maybe add it to the PR checks?

[aeneasr]

Awesome, thank you for your contribution!