Allow editing multiline prompts with external text editor (#429)

- Adds a new `Preferences` struct to the config, initially only containing `Editor: bool (default false)`.
  This struct will be serialized to configs once there is a first tea induced change to the config (eg `tea login default <name>` or `tea login add`).
- Use external editor for all multiline prompts if preferred.

We already had a function for starting a texteditor for diff reviews; it does not really make sense to replace it with `survey.Editor`, as there is a big interface mismatch: survey expects strings as inputs, while our diff functions operate on files,

fixes #424

Co-authored-by: Norwin <git@nroo.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/429
Reviewed-by: Andrew Thornton <art27@cantab.net>
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

modules/config/config.go

@@ -17,9 +17,16 @@ import (
 	"gopkg.in/yaml.v2"
 )
 
+// Preferences that are stored in and read from the config file
+type Preferences struct {
+	// Prefer using an external text editor over inline multiline prompts
+	Editor bool `yaml:"editor"`
+}
+
 // LocalConfig represents local configurations
 type LocalConfig struct {
-	Logins []Login `yaml:"logins"`
+	Logins []Login     `yaml:"logins"`
+	Prefs  Preferences `yaml:"preferences"`
 }
 
 var (
@@ -55,6 +62,11 @@ func GetConfigPath() string {
 	return configFilePath
 }
 
+// GetPreferences returns preferences based on the config file
+func GetPreferences() Preferences {
+	return config.Prefs
+}
+
 // loadConfig load config from file
 func loadConfig() (err error) {
 	loadConfigOnce.Do(func() {