Option to skip the interstitial message page after email contact form submission

[ricklecoat]

Is your feature request related to a problem? Please describe.
The thing that most drives me into the arms of 3rd party solutions for something as basic as an email contact form ({exp:email:contact_form}) is EE's insistence on putting an intermediate ‘system message’ page between the form submission and the specified ‘return’ page. One can reduce (or extend to infinity) the amount of time that this page pauses before redirecting to the return URL, but it cannot be fully eliminated. Since the generic system message template is used for this interstitial page there is a limit to the amount that it can be customised, even if fully-custom system message templates are used. Even setting the redirect= parameter to 0 sends the user to the interstitial page for a split second.

Describe the solution you'd like
Allow the value of 0 on the 'redirect' parameter of the {exp:email:contact_form} form tag to skip the interstitial page altogether. The value of 'none' can remain as it is now — to take the user to the interstitial system_message page and leave them there.

Describe alternatives you've considered
Alternatives inevitably mean 3rd party addons, but that adds technical debt to the system and risks addons being abandoned (I was going to use FormGrab, but it seems to be unsupported now). Freeform is the gold standard but it's not free, and TBH has way more functionality than I need. All I want is for the basic email form to NOT send me on a 2-step redirect when a single step is all that's required.

Teachability, Documentation, Adoption, Migration Strategy
The docs would merely need to be updated to specify that the standard sequence of events is Form submission > Message page (for period specified in params) > Return URL (if specified), and that giving a parameter of redirect="0" will change that to Form submission > Return URL. (Maybe if no return url is specified in the params and redirect="0" then the return URL becomes the site home page).

• I am capable and would like to work on implementation of this feature if it is considered.