Support for Signal Polls

[peteh]

Feature Request

According to AsamK/signal-cli#1885 signal-cli already supports the new polls feature.

It would be great if it could be exposed in signal-cli-rest as well.

I haven't found another issue regarding polls, so I hope this is the right way to request it.

[bbernhard]

Unfortunately there seems to be no documentation yet. I quickly had a glance at the signal-cli sourcecode and figured out the general functionality, but a few details aren't 100% clear to me. So, I guess it might make sense to have a look at it, once there is some documentation available.

[peteh]

Now the documentation has been added as well.