Implement wasmer config

[fschutt]

Fixes #3383.

[ptitSeb]

I would prefer a simpler:
config XXX instead of config get XXX
and
set-config XXX YYY instead of config set XXX YYY

But yeah, the switch from config --XXX is a bit strange to me, as it's the common way to query config on various linux tools (pkg-config, llvm-config, sdl2-config...).

That's just personnal taste, nothing blocking.

[syrusakbary]

wasmer config --pkg-config and others (--include-dir) should NOT live in wasmer config get in any case. wasmer config get {KEY} are for settings that can be configured by the user via the counterpart wasmer config set {KEY} {VALUE}.

We need to preserve old behavior for the previously existing config flags

[fschutt]

@syrusakbary the default config now looks like this:

wax_cooldown = 0
telemetry_enabled = false
update_notifications_enabled = false

[registry]
active_registry = "https://registry.wapm.dev/graphql"
tokens = []

[proxy]

1. Do we still need the wax_cooldown, since we don't have wax anymore?
2. We need to watch out that the switch from waom.toml to wasmer.toml is as smooth as possible:

wasmer/lib/registry/src/config.rs

Line 206 in 58ee174

toml::from_str(&config_toml).map_err(|e| format!("could not parse {path:?}: {e}"))

... will fail if we do non-backwards compatible breaking changes to the wasmer.toml. Would be better to return Self::default() here in the error case.

[syrusakbary]

Do we still need the wax_cooldown, since we don't have wax anymore?

Probably not, but we should assure that when renaming the old wapm.toml to wasmer.toml the reading doesn't crash

Changes implemented

[theduke]

LGTM, relying on @syrusakbary sign off yesterday.