Feature/multiple client notifications (BIDS-749)

[D13ce]

The following things should be considered during review/testing:

• Toggling Client Updates off should not deactivate any client toggle anymore.
• Once the app is updated, the old ETH1/ETH2-Client settings become obsolete. The settings are converted once.
• Checking for updates now is a bit smarter i.e. if you toggle a client the app only checks for an update for that client.

[manuelsc]

A bug I encountered during testing:

• Set fe Geth and Besu as execution client on the update page
• Disable client updates on notification page
• Rightly so all client updates dissappear on the beaconcha.in website
• Change execution client in the app, fe switch of geth and turn on nethermind, exit page, open again. The settings returned to the previous saved state, so Geth and Besu is still turned on, nethermind is turned off

Expected behaviour: Changing the clients on the app when client update notification setting is turned off should be possible. But not be synced with beaconcha.in.