feat: provide postgres profile

[patricebender]

this does the same as the already existing pg
profile. People can provide their service credentials and just do a cds deploy --profile postgres which is symmetrical to the cds deploy --profile sqlite

for #1471

[BobdenOs]

These credentials could be moved into the postgres kind under the [development] profile. Then both pg and postgres can just be the kind: postgres ?

[patricebender]

do we need the !? locally it doesnt make a difference, it seems.

[swaldmann]

This makes Postgres the default for all non-production scenarios though. Might be intended, but we defaulted to SQLite before so this is an incompatible change.

It's then also doing this merge of SQLite and Postgres credentials for a new project:
cds init bookshop --add sample --nodejs && cd bookshop && cds add postgres && cds env requires.db:

{
  impl: '@cap-js/sqlite',
  credentials: {
    url: ':memory:',
    host: 'localhost',
    port: 5432,
    user: 'postgres',
    password: 'postgres',
    database: 'postgres'
  },
  data: [ 'db/data', 'db/csv', 'test/data' ],
  pool: { max: 1 },
  kind: 'sqlite'
}

I propose instead you put the credentials under cds.requires.kinds.postgres, similar to how it's done in @cap-js/hana:
https://github.com/cap-js/cds-dbs/blob/main/hana/package.json#L58-L72