Implement `ALEStartAllLSPs` for starting all LSP servers early

First of all, thank you for developing great tool!

I have a question.
How to restart lsp?

ALE has 'ALEStopAllLSPs' API, but It does not seem to be that there is not start lsp API.
Sometimes, I want switch lsp each project.
So I want write vimscript like this.

```vim
function! SwitchNightlyRls() abort
if (&ft=='rust')
call ale#lsp#reset#StopAllLSPs()
call ale#Set('rust_rls_toolchain', 'nightly')
call ale#lsp#reset#StartAllLSPs() " I want this API
endif
endfunction
```

Is there way that resolve my problem?