Fix Discord API v9 issues with GuildScheduledEvent

[LeigerGaming]

This fixes the ability to use these models from the client, as they were broken due to the hyphens:

• AuditLog (replace $client->audit-log with $client->auditLog)
• GuildScheduledEvent (replace $client->guild-scheduled-event with $client->guildScheduledEvent)
• GuildTemplate (replace $client->guild-template with $client->guildTemplate)
• StageInstance (replace $client->stage-instance with $client->stageInstance)

Additionally, it fixes the parameter types for GuildScheduledEvent. For example, 'scheduled_start_time' was listed as type 'ISO8601 timestamp' because that's what the Discord API says. But it's actually a PHP string, in the format of an ISO8601-compatible date/time.

With these parameter type fixes in place, it means that it's actually possible to create an event now, using code like this:

$client->guildScheduledEvent->createGuildScheduledEvent([
    'guild.id' => $guildId,
    'name' => 'Event Name',
    'description' => 'Event Description',
    'scheduled_start_time' => '2022-01-16T07:30:00+00:00',
    'scheduled_end_time' => '2022-01-16T09:30:00+00:00',
    'privacy_level' => 2, // GUILD_ONLY
    'entity_type' => 3, // EXTERNAL
    'entity_metadata' => [
        'location' => 'https://example.com',
    ],
]);

See the relevant documentation here: https://discord.com/developers/docs/resources/guild-scheduled-event#create-guild-scheduled-event

I have successfully created events in my Discord server using this, so I can verify that it works for scheduled events.

There may be outstanding parameter type issues for AuditLog, GuildTemplate, and StageInstance. However I'll leave that to someone else to fix if there is in fact an issue.

[LeigerGaming]

Just doing some testing. I can confirm that AuditLog works as intended:

$client->auditLog->getGuildAuditLog([
    'guild.id' => $guildId,
    'limit' => 5,
]);

[BriqueAuBob]

We can access it with the following syntax:
$client->{"guild-scheduled-event"}->createGuildScheduledEvent()
for example, but that looks nicer with your solution

[LeigerGaming]

Oh! Wasn't aware of that workaround. Good to know. It occurred to me that a string might work, but I never actually tested it because I assumed I'd run into the same problem. I agree that it's nicer being able to do it without the string.

Thanks for merging it aequasi :)