Use RegisterDirectiveOrder for rate_limit before basic_auth

[steffenbusch]

I believe it would be a nice improvement if the Caddy HTTP Rate Limit Module leveraged the new RegisterDirectiveOrder feature from Caddy v2.8 (caddyserver/caddy#5865).

func init() {
	httpcaddyfile.RegisterHandlerDirective("rate_limit", parseCaddyfile)
+	httpcaddyfile.RegisterDirectiveOrder("rate_limit", "before", "basic_auth")
}

I would open a PR, but I am unsure if upgrading the go.mod requirements from github.com/caddyserver/caddy/v2 v2.7.6 to v2.8.4, along with all the other necessary updates after running go mod tidy, is acceptable for you and if it might break something for other users. I simply don't know enough about Go / Caddy module dependencies to assess this.

[francislavoie]

The minimum version required to use that is v2.8.0 so we can put that in the go.mod, though up to .4 is just bugfix releases, people shouldn't be building with an earlier patch at this point.