Implement Cobra CLI tooling, Viper config tooling (#336)

* start pulling out + replacing urfave and config

* replace many many instances of config

* move more stuff => viper

* properly remove urfave

* move some flags to root command

* add testrig commands to root

* alias config file keys

* start adding cli parsing tests

* reorder viper init

* remove config path alias

* fmt

* change config file keys to non-nested

* we're more or less in business now

* tidy up the common func

* go fmt

* get tests passing again

* add note about the cliparsing tests

* reorganize

* update docs with changes

* structure cmd dir better

* rename + move some files around

* fix dangling comma

internal/config/file.go

@@ -0,0 +1,38 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package config
+
+import (
+	"github.com/spf13/viper"
+)
+
+// ReadFromFile checks if there's already a path to the config file set in viper.
+// If there is, it will attempt to read the config file into viper.
+func ReadFromFile() error {
+	// config file stuff
+	// check if we have a config path set (either by cli arg or env var)
+	if configPath := viper.GetString(Keys.ConfigPath); configPath != "" {
+		viper.SetConfigFile(configPath)
+		if err := viper.ReadInConfig(); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}