Previously, proxy didn't forward auxiliary `options` parameter
and other ones to the client's compute node, e.g.
```
$ psql "user=john host=localhost dbname=postgres options='-cgeqo=off'"
postgres=# show geqo;
┌──────┐
│ geqo │
├──────┤
│ on │
└──────┘
(1 row)
```
With this patch we now forward `options`, `application_name` and `replication`.
Further reading: https://www.postgresql.org/docs/current/libpq-connect.htmlFixes#1287.
The new format has a few benefits: it's shorter, simpler and
human-readable as well. We don't use base64 anymore, since
url encoding got us covered.
We also show a better error in case we couldn't parse the
payload; the users should know it's all about passing the
correct project name.
[proxy] Add the `password hack` authentication flow
This lets us authenticate users which can use neither
SNI (due to old libpq) nor connection string `options`
(due to restrictions in other client libraries).
Note: `PasswordHack` will accept passwords which are not
encoded in base64 via the "password" field. The assumption
is that most user passwords will be valid utf-8 strings,
and the rest may still be passed via "password_".
