[fix](cooldown) fix cooldown datetime

[justfortaste]

Proposed changes

Issue Number: close #xxx

#16553 cooldown_ttl and cooldown_datetime cann't set at the same time. If cooldown_datetime is set, cooldown_ttl will be set to -1.
Tablet::_get_newest_cooldown_time will always get storage_policy->cooldown_datetime , then all new rowsets will be incorrectly cooldowned.

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[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[dataroaring]

if cooldown_ttl is -1, then cooldown_datetime is used, original code is right. Could you show an bad case?

[lide-reed]

LGTM

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[justfortaste]

if cooldown_ttl is -1, then cooldown_datetime is used, original code is right. Could you show an bad case?

CREATE STORAGE POLICY test_policy PROPERTIES( "storage_resource" = "xxxx", "cooldown_datetime" = "2020-10-18 12:00:00" );

the new segments will cooldown, but their time is bigger than CooldownDatetime "2020-10-18 12:00:00".

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

We're closing this PR because it hasn't been updated in a while.
This isn't a judgement on the merit of the PR in any way. It's just a way of keeping the PR queue manageable.
If you'd like to revive this PR, please reopen it and feel free a maintainer to remove the Stale tag!