Add Mastodon to social integration

[alpinho]

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
Integrate a similar feature for Mastodon personal profile as implemented for the other social platforms.

Describe alternatives you've considered
N/A

Additional context
N/A

[alpinho]

I just realized that there is already an issue (#918) opened asking for this feature. The proposed solution in the thread works for me, as well!

[alshedivat]

mastodon social link was also added in #974