docs(db): describe role concept

[evolkmann]

Highlight that the DATABASE_OWNER must actually be the owner to work as expected.

This misunderstanding on my end caused quite some delay in my project's rollout, therefore I figured that others might also run into this issue.

Description

The issue occured to me when I created the initial schema with my personal postgres user, not with the DATABASE_OWNER role. Therefore, nothing in the private schema, as well as in the graphile_worker schema was accessable.

Here is an example of another person who probably had a similar issue: https://discord.com/channels/489127045289476126/498852330754801666/779378725946130462

Performance impact

n/a

Security impact

n/a

Checklist

• [x] My code matches the project's code style and yarn lint:fix passes.
• [ ] I've added tests for the new feature, and yarn test passes.
• [ ] I have detailed the new feature in the relevant documentation.
• [ ] I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• [ ] If this is a breaking change I've explained why.

[evolkmann]

@benjie Thanks! If I had deep enough knowledge I would have written it that way, thanks for improving my text 😉