Closes #17089: Add metric to track both normal and private URI opened

[rocketsroger]

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[rocketsroger]

Request for data collection review

1. What questions will you answer with this data?
   A counter of URIs visited by the user in the current session, including page reloads.
   This includes private browsing but does not include background page requests and URIs from embedded pages.
2. Why does Mozilla need to answer these questions? Are there benefits for users? Do we need this information to address product or business requirements?

   This allows for a better assessment of the app's usage.
3. What alternative methods did you consider to answer these questions? Why were they not sufficient?

   No alternative is available to answer this question.
4. Can current instrumentation answer these questions?

   No current instrumentation can answer this question.
5. List all proposed measurements and indicate the category of data collection for each measurement, using the Firefox data collection categories found on the Mozilla wiki.

Measurement Description	Data Collection Category	Tracking Bug #
Normal and Private URI visits	category 2 - interaction data	#17089

6. Please provide a link to the documentation for this data collection which describes the ultimate data set in a public, complete, and accurate way.
   https://github.com/mozilla-mobile/fenix/blob/master/docs/metrics.md
7. How long will this data be collected? Choose one of the following:

   This is scoped to a time-limited experiment/project until date 08-01-2021.
8. What populations will you measure?

   No filters - all locales, channels, etc.
9. If this data collection is default on, what is the opt-out mechanism for users?

   Default Glean SDK opt-out mechanism.
10. Please provide a general description of how you will analyze this data.

    Glean / Amplitude
11. Where do you intend to share the results of your analysis?

    Only on Glean, Amplitude and with mobile teams.
12. Is there a third-party tool (i.e. not Telemetry) that you are proposing to use for this data collection?
    
No third-party tool will use this data.

[Amejia481]

LGTM!

[boek]

Data Review Form (to be filled by Data Stewards)

1. Is there or will there be documentation that describes the schema for the ultimate data set in a public, complete, and accurate way?
   Yes, metrics.yaml and metrics.md

2. Is there a control mechanism that allows the user to turn the data collection on and off?
   Yes, data collection settings

3. If the request is for permanent data collection, is there someone who will monitor the data over time?
   Has expiry

4. Using the category system of data types on the Mozilla wiki, what collection type of data do the requested measurements fall under?
   Type 2

5. Is the data collection request for default-on or default-off?
   Default on

6. Does the instrumentation include the addition of any new identifiers (whether anonymous or otherwise; e.g., username, random IDs, etc. See the appendix for more details)?
   No

7. Is the data collection covered by the existing Firefox privacy notice? If unsure: escalate to legal if:
   Yes

8. Does there need to be a check-in in the future to determine whether to renew the data?
   Fenix team will check-in at expiry

9. Does the data collection use a third-party collection tool?
   No

[mergify]

This pull request has conflicts when rebasing. Could you fix it @rocketsroger? 🙏