Is your feature request related to a problem? Please describe.
I'm trying to set up signature help to be triggered just as it is possible with completion (ig by <Tab> or <c-space>).

Describe the solution you'd like
Documentation for signature has:

"signature.enable":~

	Enable signature help when trigger character typed, require restart
	service on change.,  default: `true`

And for completion:

"suggest.autoTrigger":~

	How should completion be triggered,  default: `"always"`

	Valid options: ["always","trigger","none"]

That "trigger" option and function/setting similiar to inoremap <silent><expr> <c-space> coc#refresh() for signature help is what I'm looking for.

Additional context
I'm aware of signature.triggerSignatureWait.