fix(electric): Rewrite PostgreSQL URI parser

[alco]

Main improvements:

• support postgres:// scheme
• default to using the username as the database name if the latter is missing from the URI (default behaviour of psql)

Fixes VAX-1264, VAX-1265.

[linear]

VAX-1265 Electric's PG URL parsing fails on `postgres://`

Electric can only parse the postgresql:// scheme. However, some hosting providers, such as Fly.io, may use postgres://. Electric chokes on that:

$ DATABASE_URL=postgres://electric:passwordlocalhost:54321/electric iex -S mix
Erlang/OTP 25 [erts-13.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]

** (MatchError) no match of right hand side value: "postgres"
    (postgresql_uri 0.1.0) lib/postgresql_uri.ex:89: PostgresqlUri.parse/1
    config/runtime.dev.exs:15: (file)
    /home/alco/code/electric-sql/electric/components/electric/config/runtime.exs:172: (file)

[magnetised]

lovely stuff. nice to lose a dependency right.

[linear]

VAX-1264 Electric erroneously creates a replication slot named "electric_replication_out_test"

Electric generates a name for the replication slot that it creates along with a subcription by appending a custom suffix to the string "electric_replication_out". The suffix is derived from the database name which is looked up on the connection config. However, if the DATABASE_URL does not include an explicit database name, the suffix is set to "test".

I saw this when I was using Fly Postgres. The connection URI it provides looks as follows:

postgres://postgres:****ancient-pine-7827.flycast:5432

It does not include the database name because it is the same as the user name: postgres. So the replication slot name Electric generated in that case was "electric_replication_out_test".