FEAT: refactor Incident module to validate channel on command instead of in functions

[gcharest]

Right now, the SRE Bot's commands functions each validate that the bot is in an incident channel to perform commands.

This validation could be done once only when the incident_helper is invoked to validate that the bot is actually called from an incident channel, if it is necessary.

sre-bot/app/modules/incident/incident_helper.py

Line 60 in 64c5abd

def handle_incident_command(args, client: WebClient, body, respond: Respond, ack: Ack):

This way, validation is performed at the moment of calling the command instead of during the various tasks required to be performed.