make DATABASE_OPTIONS optional again

[gael-connan-cybex]

right now the database options have to be set for a postgres database.

it would be nicer if

• this was only required if you want to set your own options
• the place where you copy the default from (and ideally the only place it exists), i.e. the example file or the actual workflow file or readme, would have both default values side by side, so you dont have to go through multiple files until you found the base value you want to use as a base.

[gael-connan-cybex]

it can be considered to make even more of the database settings optional as well.