Verify ownership on beta.flathub.org

[barthalion]

Hi @romandemidov,

We're preparing for the launch of beta.flathub.org, and would like to see OnlyOffice verified as maintained by its developers. Currently, I've marked it as such manually, but it would be preferred to use one of the verification features. This can be initiated by logging it at https://beta.flathub.org/login with a GitHub account, pressing "Developer Settings" and following the instructions there.

Please let me know when it's done, so I can remove the manual verification flag.