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/interact/prompts.go

@@ -14,9 +14,26 @@ import (
 	"github.com/araddon/dateparse"
 )
 
-// PromptMultiline runs a textfield-style prompt and blocks until input was made.
-func PromptMultiline(message string) (content string, err error) {
-	err = survey.AskOne(&survey.Multiline{Message: message}, &content)
+// Multiline represents options for a prompt that expects multiline input
+type Multiline struct {
+	Message   string
+	Default   string
+	Syntax    string
+	UseEditor bool
+}
+
+// NewMultiline creates a prompt that switches between the inline multiline text
+// and a texteditor based prompt
+func NewMultiline(opts Multiline) (prompt survey.Prompt) {
+	if opts.UseEditor {
+		prompt = &survey.Editor{
+			Message:  opts.Message,
+			Default:  opts.Default,
+			FileName: "*." + opts.Syntax,
+		}
+	} else {
+		prompt = &survey.Multiline{Message: opts.Message, Default: opts.Default}
+	}
 	return
 }