Use linkTitle instead of title in menu to allow for short menue titles

[stormmaster42]

With this change, it is possible to use linkTitle in the front matter to define shorter titles shown in the page menu.

Example:

title: "My super extra very long title"
linkTitle "Long Title ..."

linkTitle defaults to title if it is not set.

[TheGroundZero]

Wouldn't it be better to do the following for backwards compatibility?

{{ with .LinkTitle }}{{ . }}{{ else }}{{ .Title }}{{ end }}

[stormmaster42]

Wouldn't it be better to do the following for backwards compatibility?

{{ with .LinkTitle }}{{ . }}{{ else }}{{ .Title }}{{ end }}

I don't think that's necessary, as LinkTitle falls back to Title if not set already.
Reference: https://gohugo.io/methods/page/linktitle/