[Enhancement:] Condition check before message check

[davidhozic]

Summary

Add a condition before message send that needs to be fulfilled for the message to be sent.
E. g., Last message in the channel must not be the bot's own message.

Basic Example

# "other" means the last message must be some other user's.
TextMESSAGE(..., constraints=[LastMessageConstraint("other")])

# "same" means the last message must be the same message.
TextMESSAGE(..., constraints=[LastMessageConstraint("same")])

# "own" means the last message must be owned by the bot.
# It can also be authored by the bot as long as it is not the same message.
TextMESSAGE(..., constraints=[LastMessageConstraint("own")])

Unresolved questions

No response