add spam filter with CAS api https://cas.chat/api

[umputun]

this PR adds a check via https://api.cas.chat/check?user_id=<id> API on a first message. If the user ID is passed, added to the approved list and won't run a check on that ID anymore

If the user is a spammer, it will be blocked permanently, and the message will be deleted. Dry mode won't remove message and won't ban, just reply with a warning.

[github-actions[bot]]

Pull Request Test Coverage Report for Build 6443919340

• 42 of 52 (80.77%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 80.372%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
app/events/telegram.go	8	10	80.0%
app/bot/spam.go	34	42	80.95%
<!--	Total:	42	52	80.77%	-->

Totals
Change from base Build 6134770322:	-0.01%
Covered Lines:	2379
Relevant Lines:	2960

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💛 - Coveralls

[umputun]

@paskal - can you take a look pls?

[umputun]

@paskal I have addressed all those except the last one (adding test). It looks like you were the one who added all the tg tests and if you can cover delete too it will be great.

[paskal]

Added a test in a separate commit.