Refactor relationships to add new backoffice endpoints

[andrewnicols]

These commits:

• add .gitignore for the uploaded media
• Renames Roommember to RoomMember
• adds ORM Relationships where they were missing
• adds cascade configuration for those relationships
• adds new endpoints for the /backoffice to get data (used in MDL-77917)

[andrewnicols]

Note: I have tested against weeklies with both behat and phpunit.

commit e77452220b268f70612b9b915179c17fc6d93173 (HEAD -> master, public/master, origin/master, integration/master)
Author: Ilya Tregubov <ilya@moodle.com>
Date:   Fri Jul 14 09:25:31 2023 +0800

    weekly release 4.3dev

diff --git a/version.php b/version.php
index c1c972ffc7..c2f3261bfa 100644
--- a/version.php
+++ b/version.php
@@ -29,9 +29,9 @@

 defined('MOODLE_INTERNAL') || die();

-$version  = 2023070700.00;              // YYYYMMDD      = weekly release date of this DEV branch.
+$version  = 2023071400.00;              // YYYYMMDD      = weekly release date of this DEV branch.
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.
-$release  = '4.3dev (Build: 20230707)'; // Human-friendly version name
+$release  = '4.3dev (Build: 20230714)'; // Human-friendly version name
 $branch   = '403';                     // This version's branch.
 $maturity = MATURITY_ALPHA;             // This version's maturity level.
➜  sm git:(master) ./vendor/bin/phpunit --testsuite core_communication_testsuite,communication_matrix_testsuite
Moodle 4.3dev (Build: 20230714), e77452220b268f70612b9b915179c17fc6d93173
Php: 8.1.15, pgsql: 14.8 (Homebrew), OS: Darwin 22.3.0 arm64
PHPUnit 9.5.27 by Sebastian Bergmann and contributors.

............................................................      60 / 60 (100%)

Time: 00:40.014, Memory: 88.50 MB

OK (60 tests, 179 assertions)
➜  sm git:(master) ./vendor/bin/phpunit --testsuite core_communication_testsuite,communication_matrix_testsuite
Moodle 4.3dev (Build: 20230714), e77452220b268f70612b9b915179c17fc6d93173
Php: 8.1.15, pgsql: 14.8 (Homebrew), OS: Darwin 22.3.0 arm64
PHPUnit 9.5.27 by Sebastian Bergmann and contributors.

............................................................      60 / 60 (100%)

Time: 00:42.473, Memory: 88.50 MB

OK (60 tests, 179 assertions)