Feature request: Dimension metric abnormalities

Nobody has claimed this yet.

Great news: We may soon have an Exclude by dimensions tool, which will help bot visits from getting registered as regular visits, offering to identify and block them via dimensions, such as resolution, country and browser version:
- #162

We could help the user with these tasks:
1. Discover relevant dimension patterns of cloaked bots
1. Create "Exclude by dimension"-rules to block bot visits

## Proposal

Cloaked bots usually share certain dimensions, like resolution, country and browser version, and we could offer a new "Dimension metric abnormalities"-widget to more easily discover these dimensions, and make a Matomo administrator aware of the characteristics of a potential bot attack.

**Dimension metric abnormalities widget**

All dimensions could be monitored behind the scenes, and if a dimension metric (like a specific resolution) makes a huge jump, it would be immediately obvious.

It could be exposed in a new Dashboard widget like below, which admins can add to the front page:

> ## Dimension metric abnormalities
> Dimension | Unique visitors
> :---|---:
> Resolution: 375x812 | +2.100%
> Configuration: Chrome Mobile | +1.160%
> Country: Bangladesh | +890%
> Country: Myanmar | +610%
> Country: USA | +20%

**Create Dimension metric abnormalities rule link**

At the bottom of the widget, there could be a "Create Exclude by dimension rule with top 3" link to the new "Exclude by dimensions"-feature, with these value pre-selected, ready to click "Save":

Resolution: 375x812
--AND
Configuration: Chrome Mobile
--AND
Country: Bangladesh

The link could be something along these lines:
`https://example.org?segment=resolution==375x812;countryName==Bangladesh;browserName==Chrome%2520Mobile&method=TrackingSpamPrevention.setDataSubjects`

Since Myanmar (number 4) is also relevant, the preset rule under the TrackingSpamPrevention section could be expanded to include that as well by the admin like this:

Resolution: 375x812
--AND
Configuration: Chrome Mobile
--AND
--Country: Bangladesh
----OR
--Country: Myanmar

Start by reviewing the related exclude-by-dimensions work in #162 and the TrackingSpamPrevention.setDataSubjects entry point mentioned in the proposal. Define how the Dimension metric abnormalities dashboard widget should detect and display abnormal dimension values, and how its top-three link should preselect exclusion rules. Done means the widget, rule link, and administrator-controlled country grouping work together as described.

Written by the indexing model from the issue text.