Create baseline self-service bot interaction

Build support for self-service interaction with the Discord bot. Start with two input adapters and one output adapter:

• DiscordBotCommandInputAdapter: receive a bot command from specific channels to initiate bot interaction
• DiscondBotDMOutputAdapter: respond to initial channel bot command by opening a DM to the instigating user
• DiscordBotDMInputAdapter: parse a command from a DM to the bot, respond in the same DM

Do not implement the command processing in the adapters; pass to a separate overall pipeline to parse and process the command, then relay to the outputs

While creating the baseline, refactor the Discord* adapters to ensure that only one Discord connection / instance is maintained for all Discord I/O.