Add addDate function for compatibility with MySQL

[evillique]

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• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Add addDate function for compatibility with MySQL and subDate for consistency. Reference #54275

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

[robot-ch-test-poll4]

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[rschu1ze]

Maybe test what happens if addition moves the result beyond the bounds of the date time type?

[evillique]

The behavior will be the same as in the case with the + or - operations: 1900-01-01 00:00:00.000 with the required precision.

In MySQL we simply get NULL. Should we try to replicate this behavior?

[rschu1ze]

So, if the result is outside the bounds of the data type, we say that the result is undefined.
The same semantics is used in makeDate(): https://fiddle.clickhouse.com/e58005b1-95f7-49fd-9989-10e295bfb82f

In my view, there is no need to replicate MySQL's behavior, it is more important to stay consistent within ClickHouse's functions and it's an edge case anyways.

[rschu1ze]

Lgtm, except the remaining small comments.