Builds the CalendarSourceResolver that binds a calendar source per identity: Teams
identities read their Graph calendar through the Communication MS Graph provider, authenticated
with the bot's own token (no client secret, no default mailbox: the identity names the calendar).
Builds the CalendarSourceResolver that binds a calendar source per identity: Teams identities read their Graph calendar through the Communication MS Graph provider, authenticated with the bot's own token (no client secret, no default mailbox: the identity names the calendar).