feat(model): Implement user applications

[Erk-]

This pr implements the newly added user applications, this have had some testing done, but is still missing quite a bit of documentation and maybe a bit of bike-shedding about type names and/or layout.

[laralove143]

there were too many

nit: these should be sorted alphabetically

comments so i stopped repeating them on every instance, besides that there are just things to discuss

[laralove143]

do we really need the complexity of generics here, we could follow ddocs and create a AuthorizingIntegrationOwners struct with fields kind: ApplicationIntegrationType and id: AuthorizingIntegrationOwnerId where AuthorizingIntegrationOwners is an enum with Guild(Option<Id<GuildMarker>>) and User(Id<UserMarker>)

[Erk-]

It is not a enum, instead if we should do it as in the docs we should have a hashmap with 2 possible enum keys and then different Id type depending on if it is one or the other, I think this is the easiest way to make it work nicely.

[laralove143]

i think we're adding complexity to be DRY here, i think it's worth a few added LOC to separate ApplicationIntegrationMap to different structs such as:

// for InteractionMetadata and Interaction
enum AuthorizingIntegrationOwners {
    GuildInstall(AuthorizingIntegrationOwnersGuild),
    UserInstall(Id<UserMarker>),
}

enum AuthorizingIntegrationOwnersGuild {
    Guild(Id<GuildMarker>),
    Dm,
}

and for ApplicationIntegrationTypeConfig, unless im missing something we only ever use it as ApplicationIntegrationMap<ApplicationIntegrationTypeConfig> so we can just unnest it

[Erk-]

I think this is ready for a wider review.