Instead of sending the 'injected bot_config' upon handshake, create a new swarming_bot.zip per bot group.

This will solve one challenge: when the bot start up, it'll immediately self-update with the injected one, then when the bot starts, it's already using the right bot.

This removes the 'one single executable to rule them all' for all the bots but I think it makes sense from a PoV of fleet scalability.

One challenge is that there is not one canonical bot version anymore, which has implications in the DB schema, APIs and Web UI.

One challenge is to decide if it is the best incremental route towards when bot_config is out of process. Not sure about it.