Before this commit:
- UTM campaigns are accessible for all internal users, but with email
  marketing related modules installed, if user who does not have rights
  for email marketing tries to access the campaign, an AccessError is
  raised. It's because few fields related to email marketing are added
  in model `utm.campaign` which are accesible only to the marketing
  users.
- When the user is having `mass_mailing.group_mass_mailing_campaign`
  group enabled but no rights for email marketing, the root menu of
  for the 'Email Marketing' app is visible to that user, which is
  not correct.

With this commit:
- While adding marketing related fields to the campaign, we provide the
  group("mass_mailing.group_mass_mailing_user") at field level whenever
  neccessary so it doesn't raise AcessError. Also, we show those fields
  on the campaign views only when `mass_mailing.group_mass_mailing_campaign`
  group is enabled for the user. To do this, a compute field has been
  introduced to make sure that user has rights to access email marketing
  as well as the feature to manage mass mailing from campaigns is enabled.
  The reason behind introducing a new compute field is, at view level,
  it is not possible to check that user is having multiple groups.
- We've applied the group "mass_mailing.group_mass_mailing_user" on the
  root menu of Email Marketing app, so if the user has UI only group
  "mass_mailing.group_mass_mailing_campaign" and but no rights for
  email marketing, the root menu won't won't appear.

TaskID-2417993

closes odoo/odoo#74113

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>