[feat] Button to download current & old log files

[Nerivec]

Is your feature request related to a problem? Please describe.

Some setups don't make it particularly easy to retrieve log files.

Describe the solution you'd like

A button in Tools to download the current log file.
Also possibly a button to load a list of older log files, with accompanying buttons to download them too (or some other fashion to achieve this).

[LaurentChardin]

Just a side note here : websockets are not really the best solution to manage this use case, and z2m-frontend is mostly interacting with ws/wss so far (streaming chunks of logs currently).

I would suggest to :

1. add a new HTTP-based API in z2m to manage file downloads (list/download)
2. implement a z2m-frontend button to request those files through regular HTTP file transfers