Add 30 sec. countdown on the Browser Assistant icon (during `Do not filter for 30 seconds`)

#### Hi, :wave:
 
It might be a good idea IMHO to display the 30 second countdown on the extension icon, when using the `Don't filter for 30 seconds` option.

Useful, as we don't know where we are in time when we close the Browser Assistant popup and use the website. :relaxed:

:small_blue_diamond: **Possible subtlety:** trigger its display only when the popup is closed. This, in order to prevent a double display of the countdown while the popup is still open — i.e. on the extension icon + in the popup. And … leave it or not on the extension icon if/when the popup is reopened (up to you).
 

## Visual rendering

###### :arrow_right_hook: _Like this but with a gray shield and displaying `19s` instead — if there are `19s` left in the countdown for example. :hourglass_flowing_sand:_

:information_source: **Versus blocking counter visually?** In addition to the presence of the character "s", and the decrease every second clearly recognizable, all this in addition on a _gray_ shield in this situation and as a result of the user's _immediate own action_, to be possibly even more visually distinct from a possible/probable future blocking counter — already present in `AdGuard Browser extension` —, just change the background color + text color + possibly _round_ the corners or display it within a circle or an oval instead. And/Or … either display at his side an _animated-or-not_ hourglass (:hourglass_flowing_sand:) or a vertical bar (such as a capital i) that decreases from top to bottom, or instead, if displayed within a circle, simply animate the "unfilling" of the border of the circle itself to show that a countdown is in progress.

:bulb: **Future-proof:** Once the `30s` delay is over, the shield will turn green again (once [this issue](https://github.com/AdguardTeam/BrowserAssistant/issues/79) is fixed though) and … a potential future blocking counter will take over instead. To count the new blocked XHR & co requests for example. Not incompatible with the future, therefore. :heavy_check_mark:

 
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#### _Thank you in advance. :thumbsup:_
_Environment_
**Browser Assistant** 1.3.13 on **Firefox** 103.0.2
**AdGuard** 7.10.2 on **Windows** 10 Pro 21H2 (OS Build 19044.1865)