Variants of coordinator FW with 921600 baudrate.

[antst]

@Nerivec , I added "_uhb" manifests with 921600 baud rate. but only for devices with HW flow control.
If you want to keep it together with yours, merge it.
Though, I am unsure myself, that is it good or bad idea.
From one side, it is nice to have options, but from other, it might be confusing for people. Especially, talking into account that one need to know that it is required to set proper baudrate in Z2M.

[Nerivec]

Releases are already too big (over 30 GBLs).
I think what I might do is create a separate branch where I run higher baudrates, and more advanced users can pick from the action runs (can link from release notes).
Need to establish what baudrates are viable long term before doing any of this though.