Add new transition form

[jkempster34]

Note

This is not the finished article, this is for us to refine as we learn more about how it will be used.

https://trello.com/c/3NYAPZs4

Add constants for global and special redirect types

We want to add a new site form. In order to do this we will need an easy way to
access these values.

We might want to consider refining these further into enums, as this would
allow us to remove some of the methods in the site model.

Add routes for site creation

We want to add sites per organisation.

This add nested routes for site creation.

Add site form object

We are aiming to archive Transition Config which is currently used to create
sites in Transition.

This adds a form object for the creation of a site.

It's worth noting that the process currently moves existing hosts and aka hosts
to the new site if they already exist (see
lib/transition/import/site_yaml_file.rb). We aren't yet sure whether we want
to create a new UI for that functionality, or to use this form. For now, this
form does not have that functionality.

Only validate presence of canonical host or aka if hostname is present

If hostname is not provided for the host, this validation will raise an error.

Add a condition that this validation only runs when hostname is present.

Add site creation actions and views

We are aiming to archive Transition Config which is currently used to create
sites in Transition.

This adds the actions and views necessary for a user to add a new transition.

Validate that host hostname is lowercase

Currently the site importer (lib/transition/import/site_yaml_file.rb)
downcases any hostnames.

This adds validation to the host model which will be surfaced on the new site
form.

Only allow Site managers to create new sites

This adds authorization that only people with the Site manager role in GOV.UK
Signon can create new sites.

This is so that we can safely test new features before we officially archive
Transition Config.

Validate that global new URL is absent if the global type is "archive"

Currently, there is validation in place to prevent the creation of sites which
have a global type of "redirect" without a global new URL, but the opposite
validation is missing.

Improve appearance of radio buttons

In order to style these using Bootstrap, we need to provide a block to collection_radio_buttons.

Nilify blanks on the Site model

The optional fields of the site form come through as empty strings when left
blank. These are then saved in the database, when ideally these would be saved
as nil in order to preserve the previous behaviour of adding them through
Transition Config for consistency.

We already have a module that handles the nilification of blanks, however we
need to make a couple of changes:

• We add an "except list" of attributes that we don't want to nilify, such as
  Booleans that should be false and not nil (false.blank? == true).
• We allow blank for special_redirect_strategy as this will now be nilified
  before save.

Add hints to new site form inputs

This copies the guidance fro Transition Config over to the new site form.

This will need later refinement.

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[JonathanHallam]

Can we just not downcase the host before we send it on?

[JonathanHallam]

Really like this, thanks Joe, only comment is wondering whether there's a way we can let people know what all of the fields are and maybe give a link for the tna timestamp section? Maybe lets have a chat offline?

[JonathanHallam]

Given the caveat of improving this as we go on, I'm happy with this for now, great work :)