Async upload providers

[ginkoid]

At the moment, all upload providers are loaded synchronously with require():

rctf/server/uploads/index.ts

Lines 11 to 13 in 163e25b

	// FIXME: use async loading
	// eslint-disable-next-line @typescript-eslint/no-var-requires
	const ProviderClass = require(path.join('../providers', name)).default

We should use import() instead, such as in email providers:

rctf/server/email/index.ts

Line 20 in 163e25b

const { default: Provider } = await import(path.join('../providers', emailConfig.provider.name)) as { default: ProviderConstructor }