Implement proper support for npgsql7

[fbjerggaard]

Fixes #182

Replaces #183

Requires some documentation changes:

Configure with

builder.Services.ConfigureEventuousPostgres(connString)
// or
builder.Services.ConfigureEventuousPostgres(connString, pgOptions)

instead of

NpgsqlConnection GetConnection() => new(connectionString);

builder.Services.AddSingleton((GetPostgresConnection)GetConnection);

All tests are passing

[alexeyzimarev]

Sorry for a delay with merging this, I was long under an impression that it's still a draft. Is it ready? Can I merge it now?

[fbjerggaard]

No worries - I could have written that it was ready.

I have been using it in a test environment for the past month, and so far it seems to be working as intended and all tests are passing, so it should be good to merge