[2.x] Add support for pgsql's search_path

[johannsa]

Current Behavior

Note: This only applies to the pgsql driver!

Can we, please, add support for specifying and using a database schema other than the default "public"?

In the back of this issue, I am submitting a PR with some changes I propose to achieve that.

Steps to Reproduce

1. Start a new install.
2. Select the PostgreSQL driver.
3. Observe:
   • There is no field to specify the schema to be used in the database (it will use the "public" schema by default).
4. Fill the form.
5. Install.
6. Observe:
   • It used the "public" schema by default.

Expected Behavior

The user should be able to specify and use a database schema other than the default "public".

Screenshots

(Proposed change)

Environment

• Flarum version: 2.0.0-beta.3
• Website URL: N/A
• Webserver: Nginx
• Hosting environment: WSL
• PHP version: 8.4.10
• Browser: Edge 140

Output of php flarum info

johann@DESKTOP1:~/websites/REDACTED/flarum$ php flarum info
Flarum core: 2.0.0-beta.3
PHP version: 8.4.10
PostgreSQL version: PostgreSQL 17.5 (Debian 17.5-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
Loaded extensions: Core, date, libxml, openssl, pcre, zlib, filter, hash, json, pcntl, random, Reflection, SPL, session, standard, sodium, mysqlnd, PDO, xml, calendar, ctype, curl, dom, mbstring, FFI, fileinfo, ftp, gd, gettext, iconv, intl, ldap, exif, mysqli, pdo_mysql, pdo_pgsql, pdo_sqlite, pgsql, Phar, posix, readline, shmop, SimpleXML, sockets, sqlite3, sysvmsg, sysvsem, sysvshm, tokenizer, xmlreader, xmlwriter, xsl, zip, Zend OPcache, xdebug
+----------------------+---------+--------+
| Flarum Extensions    |         |        |
+----------------------+---------+--------+
| ID                   | Version | Commit |
+----------------------+---------+--------+
| flarum-flags         | 2.x-dev |        |
| flarum-approval      | 2.x-dev |        |
| flarum-tags          | 2.x-dev |        |
| flarum-suspend       | 2.x-dev |        |
| flarum-subscriptions | 2.x-dev |        |
| flarum-sticky        | 2.x-dev |        |
| flarum-statistics    | 2.x-dev |        |
| flarum-mentions      | 2.x-dev |        |
| flarum-markdown      | 2.x-dev |        |
| flarum-lock          | 2.x-dev |        |
| flarum-likes         | 2.x-dev |        |
| flarum-lang-english  | 2.x-dev |        |
| flarum-emoji         | 2.x-dev |        |
| flarum-bbcode        | 2.x-dev |        |
+----------------------+---------+--------+
Base URL: http://REDACTED
Installation path: /var/www/REDACTED/flarum
Queue driver: sync
Session driver: file
Mail driver: mail
Debug mode: off

Possible Solution

In the back of this issue, I am submitting a PR with some changes I propose to achieve that.

Additional Context

No response