Display a helpful error message when the sync device limit is reached

[fmarier]

There is currently a server-enforced limit of 50 devices per sync chain. At the moment, joining a full chain will trigger a generic error.

We should display a more helpful error message that explains the problem.

[fmarier]

My suggestion:

This Sync chain is full and it's not possible to add more devices to it. Please remove any unused devices before trying to join this Sync chain.

[rmcfadden3]

This Sync chain has reached its device limit. To add a new device, please first remove any unused devices.

or

This Sync chain has reached its device limit. To add a new device, please first remove any unused devices and then try syncing again.

[fmarier]

Thanks @rmcfadden3 . Let's go with the first option:

This Sync chain has reached its device limit. To add a new device, please first remove any unused devices.

[bsclifton]

Related https://github.com/brave/brave-browser/issues/27929