Propose the "Safari certificate" installation for all macOS users

[Xayton]

With #927 the Arduino Agent can now ask users to install the HTTPS certificate needed when using Safari on macOS. This is asked only once and only if the user has Safari as the default browser.

We continue receiving report of users having problems get the agent working, particularly inexperienced ones that don't know what the agent is, and how it works.

We think it could help ask all users, and not only ones that have Safari as the default browser, to install the HTTPS certificate. This would be asked using the existing mechanism, and would be asked only once.
Note: this is being discussed internally, as it could be a slight annoyance to non-Safari users, or could promote the installation of a root HTTPS certificate that would not be needed otherwise.

• Evaluate the change, and decide if we want to implement it or not.
• Ask all macOS users, that have not received the notification already, if the want to install the HTTPS certificate.
• This activity should be done with or after Clarify the HTTPS certificate functionality #958 is completed.