add alternative configurability for view visibility and condition to users

[Mariusthvdb]

currently we can allow a user or set of users to see a view:

    visible:
      - user: 123...
      - user: 456...
      - user: 789...

We need to do this per view to enable those users on each of those views. This is fine, but very basic and limited. added to that, with several dashboards and many views, configuring those requires a lot of (repetitive) yaml. And we dont have a central overview, but need to check each and every view.

please consider adding configuring the views like the former Custom Header did. This was based on a generic show_tabs template ```

show_tabs: >-
  {% if is_state('input_select.mode','Developer') %}0 to 12
  {%- else -%}0 to 4, 5, 6 to 12
  {%- endif -%}

and allowed several conditions (or exceptions) like:

exception:
  - conditions:
      user: 123.., 456..., 789...
    config:
      show_tabs: 0 to 4, 6, 8 to 12

or eg allow per device user agent

  - conditions:
      user_agent: iPhone

Not sure if I understand what is written about conditions on https://next.home-assistant.io/lovelace/views/#options-for-visible but the above example would at least give us these options.

all in all, only a few lines for great configurability and central overview.

please consider.