Add an API for adding an item before the siteSecurityIconView on the toolbar

[Amejia481]

We are going to need that for a new feature of tracking protection on Fenix. We want to have a item view before the siteSecurityIconView. mozilla-mobile/fenix#3901

┆Issue is synchronized with this Jira Task

[Amejia481]

@pocmo in term of API. Do you think we need something similar to navigationActions?

    //   +-------------+------+-----------------------------------------+
    //   | navigation  | icon |                                         |
    //   |   actions   |      |                                         |
    //   +-------------+------+-----------------------------------------+

1) Instead of having just one icon item, could we have a list of items in its place and having the siteSecurityIcon inside of that list?

+-------------+------+-----------------------+----------+------+
| navigation  |icons | url       [ page    ] | browser  | menu |
|   actions   |      |           [ actions ] | actions  |      |
+-------------+------+-----------------------+----------+------+

2) Option 2 would be overkill, adding an additional item would be enough?

+-------------+------+-----------------------+----------+------+------+
| navigation  |shield| icon | url       [ page    ] | browser  | menu |
|   actions   |      |      |           [ actions ] | actions  |      |
+-------------+------+-----------------------+----------+------+------+