Pkg.Registry.update(): add throw_on_error kwarg

[DilumAluthge]

Fixes #4244

This PR adds the optional throw_on_error kwarg to the Pkg.Registry.update() function.

The default value is throw_on_error = false, which preserves the existing behavior by default.

However, if the user opts-in by specifying throw_on_error = true, then if Pkg.Registry.update() encounters an error, we will throw an exception.

The name throw_on_error can be bikeshedded.

[DilumAluthge]

Hmmm. I think I should wait until the end, instead of throwing immediately.

[KristofferC]

I don't really like this because Registry.update is automatically called in various places and you don't want the pkg operation to completely fail if one of the registries fail to update. For example, if you do Pkg.add("Plots") and some test registry fails to update you still want to install plots.

[Keno]

In particular, the network might be down, but you still want to do the Project.toml modification.

[DilumAluthge]

How about we set throw_on_error = false by default? So then, by default, people will get the existing behavior, but people can opt-in by specifying throw_on_error = true?

@omus I think that would still solve your use case, right?

[DilumAluthge]

How about we set throw_on_error = false by default? So then, by default, people will get the existing behavior, but people can opt-in by specifying throw_on_error = true?

I have implemented this.

[omus]

I'm onboard with this change. My in my use case I want this to fail fast to avoid spending time on adding packages when it will eventually fail

[omus]

Do we want to both have an @error and an exception?

[omus]

Maybe could be:

Suggested change

	function update(regs::Vector{RegistrySpec}; io::IO=stderr_f(), force::Bool=true, depots = [depots1()], update_cooldown = Second(1), throw_on_error = false)
	function update(regs::Vector{RegistrySpec}; io::IO=stderr_f(), force::Bool=true, depots = [depots1()], update_cooldown = Second(1), strict::Bool=false)

We already have a Pkg.precompile(; strict::Bool=false) which reminds me of this

[DilumAluthge]

Maybe could be:

We already have a Pkg.precompile(; strict::Bool=false) which reminds me of this

I think that strict would be fine, especially if we already use strict in other places.

So the options that we are considering are:

1. throw_on_error
2. strict

Are there any other options that we can think of?

[IanButterworth]

I think just throw is enough. I think that's used elsewhere.