@uppy/aws-s3-multipart: add support for signing on the client

[aduh95]

This adds opt-in support for signing on the client (the default is on the server). This works for both multipart and non-multipart uploads.
Implementers should opt-in into this only if they are confortable giving end users direct access to signing files for their bucket. It decreases by about 20% the upload for both multipart and non-multipart.

We might want to make the Companion changes more configurable, however it can happen in a follow up PR.

[Murderlon]

we could type this more strictly to only allow boolean if companionUrl is set. It's a bit more involved but here is an example:

uppy/packages/@uppy/transloadit/types/index.d.ts

Lines 116 to 153 in 7a90f9b

	export type TransloaditOptions = Options &
	(
	| {
	assemblyOptions?: AssemblyOptions | ((file?: UppyFile) => Promise<AssemblyOptions> | AssemblyOptions)
	/** @deprecated use `assemblyOptions` instead */
	getAssemblyOptions?: never
	/** @deprecated use `assemblyOptions` instead */
	params?: never
	/** @deprecated use `assemblyOptions` instead */
	fields?: never
	/** @deprecated use `assemblyOptions` instead */
	signature?: never
	}
	| {
	/** @deprecated use `assemblyOptions` instead */
	getAssemblyOptions?: (
	file?: UppyFile
	) => AssemblyOptions | Promise<AssemblyOptions>
	assemblyOptions?: never
	/** @deprecated use `assemblyOptions` instead */
	params?: never
	/** @deprecated use `assemblyOptions` instead */
	fields?: never
	/** @deprecated use `assemblyOptions` instead */
	signature?: never
	}
	| {
	/** @deprecated use `assemblyOptions` instead */
	params?: AssemblyParameters
	/** @deprecated use `assemblyOptions` instead */
	fields?: { [name: string]: number | string } | string[]
	/** @deprecated use `assemblyOptions` instead */
	signature?: string
	/** @deprecated use `assemblyOptions` instead */
	getAssemblyOptions?: never
	assemblyOptions?: never
	}
	)

What do you think?

[aduh95]

Good thinking, I think it should go on its own PR, because the other options (e.g. signPart, abortMultipartUpload, etc.) would also benefit for more fine-grained typings.

[Murderlon]

Looking very good!