Drop the git config cache when getting focus

This allows changing git config values while lazygit is running (e.g. in a
different terminal tab, or even in lazygit's ":" shell prompt), and have them
take effect immediately, while still getting some benefit from caching them
while lazygit is in the foreground.

pkg/commands/git_commands/config.go

@@ -111,3 +111,7 @@ func (self *ConfigCommands) GetCoreCommentChar() byte {
 func (self *ConfigCommands) GetRebaseUpdateRefs() bool {
 	return self.gitConfig.GetBool("rebase.updateRefs")
 }
+
+func (self *ConfigCommands) DropConfigCache() {
+	self.gitConfig.DropCache()
+}