postgres: Expand grant privileges where required

[iainlane]

Inside postgresql, some privileges are altered when issuing a GRANT, for example ALL is expanded to CREATE, TEMPORARY, CONNECT.

When we observe the grant, we query privileges on the database to see if the ones in the grant exist. Given that they are expanded, we can't simply query for what the user gave us. Expand the privileges which need expanding before we make the query.

Closes: #92

How has this code been tested

• There's a unit test to check the permissions are expanded
• We extracted the queries the provider is using and ran them manually against a database

[Duologic]

The unit test seems to fail, mind having a look @iainlane ?

[iainlane]

Hmm, it works here 🤔

I'll take a look later and see if CI does something different to me.

[iainlane]

@Duologic I found the cause, nondeterministic map iteration order, should be fixed in e761eaa, could you take a look please?