Support building an allow-list of providers (#527)

* Add providers subcommand to verify providers

Allows users to check what providers are available

* Fix version output to add new line

This command was totally broken until we moved around the call to
`initConfig()`, this just fixes the output now that it works.

* Flip boolean of provider include tags

All providers are still included by default and fix tags using the old
format.

scripts/process_build_tags.sh

@@ -0,0 +1,56 @@
+#!/bin/bash
+
+# set -e -o pipefail
+
+orig_tags=(${@})
+new_tags=()
+omit_providers=()
+
+let found_provider=0
+
+function debug() {
+	if [ "${V}" = "1" ]; then
+		(>&2 echo "$@")
+	fi
+}
+
+for tag in ${orig_tags[@]}; do
+	case "${tag}" in
+	no_*_provider)
+		# filtered
+		debug "filtered old, invalid ${tag} from tag list, provider is already excluded"
+
+		# store just in case no "proper" provider tags were provided
+		# In such cases we'd build everything, but we don't want to build these
+		p="${tag#no_}"
+		p="${p%_*}"
+		omit_providers+=("${p}")
+		;;
+	*_provider)
+		found_provider+=1
+		new_tags+=("${tag}")
+		;;
+	*)
+		new_tags+=("${tag}")
+		;;
+	esac
+done
+
+if [ ${found_provider} -eq 0 ]; then
+	# include all providers
+	for i in $(ls providers/register/provider_*.go); do
+		p="${i#*provider_}"
+		p="${p%.*}"
+
+		if [[ ! "${omit_providers[*]}" =~ "${p}"  ]]; then
+			debug "including provider ${p}"
+			new_tags+=("${p}_provider")
+		else
+			debug "excluding provider ${p}"
+		fi
+	done
+fi
+
+
+
+echo "${new_tags[@]}"