Usage statistics info and opt-out

[mshabarov]

Provides general info about usage statistics and ways to opt-out.

Related-to vaadin/flow#21217

[github-actions]

AI Language Review

• In the section about optimizing the bundle, consider rephrasing "components aren't used, but only third-party components are utilized" to "components are not used, but third-party components are utilized" for consistency in style.
• Ensure consistent formatting in sentences by replacing contractions like "won't" with "will not."
• In the section "Easier Debugging," consider specifying the recommended configuration parameter more clearly, possibly by separating it into a distinct paragraph for clarity: "This mode is used when the configuration parameter frontend.hotdeploy is set to true."
• For the section on Usage Statistics, clarify the instructions for setting the system property or environment variable by specifying: "set the vaadin.devmode.usageStatistics.enabled system property to false" and "set the VAADIN_USAGE_STATS_ENABLED environment variable to false."

[tltv]

vaadin-usage-statistics component is imported by default (at least in development mode). If I read this first time, my first assumption would be that setting vaadin.devmode.usageStatistics.enabled or VAADIN_USAGE_STATS_ENABLED would automatically also stop importing vaadin-usage-statistics (or disable it) automatically.
Now disabling requires two steps. And seems that the instructions in vaadin-usage-statistics regarding global disabling with a script is broken.
And additionally Flow projects may not have package.json to put disableUsageStatistics flag. Which would make opting-out not possible by following the current instruction.

[mshabarov]

Can we make it in steps: add the server-side opt-out docs and option for environment variables, then take a look at the client-side parameter, what is broken and add docs later?

[mshabarov]

So I removed the mention about vaadin-usage-statistics so far to unblock vaadin/flow#21217.

[tltv]

Sure it can be done in steps. Also disabling telemetry on server side should ideally also remove or disable vaadin-usage-statistics automatically. That should be also one step.