[IMP] mail, mass_mailing : apply blacklist, opt_out per mailing list

Purpose
=======
- Apply the blacklist implementation to Improve mailing subscription to be more
  compliant with the European GDPR law. Keep a list of people who does not want
  to receive promotional emails (or mass mailing in general) anymore.
- Allows the recipient to update himself his mailing preferences

Specifications
===========
This commit is regrouping some main changes on mass mailing.
  Apply Blacklist for following models through blacklist.mixin :
    - crm.lead
    - res.partner
    - mail.mass_mailing.contact
    - mail.channel.partner
- Opt_out per mailing list instead of per mailing contact.
- Replace opt_out by blacklist in crm.lead + res.partner models
- Added 'ignored' state for mass_mailing. Ignored = blacklisted, opted-out
  Ignored email are not included into final statistics to avoid confusion.
- Unsubscribe(d) pages migrated from website_mass_mailing to mass_mailing module
  as thoses pages should work without having the website module installed

Detailed implementation
===================
Mass-mailing :
	- A blacklisted email is notified by the ban icon next to the email field.
	  (at the left of the email field for display purpose)
	- Renaming the '_get_blacklist' method that was actually
	  searching opt_out list into 'get_opt_out_list'
	- Opt out per mailing list : Add opt_out + related fields (for display and
	  ergonomy reasons) on the relational model
	- Display relational model tree view instead of mass_mailing.contact tree
	  view when clicking on mass_mailing_list in kanban view
	  -> In order to be align between contact_nbr displayed in kanban tile and
	     the content of the tree view
	  -> mass_mailing contact is accesible via the user icon in this tree view
	- Remove custom filters 'filter_contact_subscription' and
	  'filter_contact_unsubscription' as opt_out is not on mass_mailing.contact
	  model anymore
	- Add 'is_public' to mailing list
	    The name of this mailing list can be seen (or not) by recipient in
	    the unsubscription page
	    If the mailing lists used in the mass mailing are not public,
	    the user in only informed that he has been unsubscribed.
	    If the mailing lists are public, the user is informed that he has been
	    unsubscribed from the mailing lists
	    and he has the choice to modify his subscription to all the public
	    mailing list he is or was subscribed to.
	- Unsubscription Page :
		- mass_mailing_contact :
		  Opt_out per mailing list, done by email and not by id, as multiple
		  contact can have the same email
		  The recipient can add/remove himself to/from the blacklist
		  The recipient can send a feedback about why he unsubscribed
		- crm.lead + res.partner :
		  Once the recipient unsubscribe, he is automatically blacklisted
		  The recipient can 'Come back' and remove himself from the blacklist
		  if he changes his mind
		- Show blacklist button parameter added in config :
		  The idea is to enable/disable the fact that the recipient can add
		  himself to the blacklist by showing or not the 'blacklist me' button
		  Only applies for mass_mailing.contact. The recipient, once
		  blacklisted, can always, no matter the value of this parameter,
		  'come back' and unblacklist himself

crm.lead + res.partner :
	- Replace opt_out by blacklist in crm.lead + res.partner models.
	  As when a res.partner or crm.lead unsubcribe, we assume that the recipient
	  does not want to receive mass mailing anymore, at all, even if we adds him
	  to a mailing list afterwards. He is then blacklisted to avoid this.
	  With this behaviour, if a new lead is created with the same email address,
	  he won't be able to receive mail in mass_mode.
	  But he will still be able to receive '1 to 1' direct email.

Task ID 33224
Closes #25966