feat(install): add --keepsrc to keep pkg/ and src/ directories (#2272)

* feat(install): add --nocleanbuild to keep pkg/ and src/ directories for
AUR packages

Providing this flag during installation of AUR packages allows for keeping
the src/ and pkg/ directories produced my makepkg. If the user wants to
delete the directories, they can either select to cleanBuild in the
cleanmenu or run the installation without the --nocleanbuild flag (yay
will only remove the directories if the package is rebuilt)

* fix(completion): simplify description for --nocleanbuild in fish

This makes the description consistent with the descriptions in the
man page, --help, and zsh completion.

* refactor(install): Rename --nocleanbuild to --keepsrc

This naming scheme is more familiar to users since it is the name of the
flag in Paru.

---------

Co-authored-by: jguer <me@jguer.space>

pkg/sync/workdir/aur_source.go

@@ -32,7 +32,11 @@ func (e *ErrDownloadSource) Unwrap() error {
 func downloadPKGBUILDSource(ctx context.Context,
 	cmdBuilder exe.ICmdBuilder, pkgBuildDir string, installIncompatible bool,
 ) error {
-	args := []string{"--verifysource", "--skippgpcheck", "-Ccf"}
+	args := []string{"--verifysource", "--skippgpcheck", "-f"}
+
+	if !cmdBuilder.GetKeepSrc() {
+		args = append(args, "-Cc")
+	}
 
 	if installIncompatible {
 		args = append(args, "--ignorearch")