Add deprecation for StringFilter format option

[VincentLanglet]

Subject

I am targeting this branch, because BC.

I already found weird the format option of the StringFilter.
If I look for something containing foo, there is IMHO no multiple way to check for this. It always LIKE %foo%.

Now, this option is weirder since we have the START WITH and an END WITH checks.
Why would these checks be made with %foo and foo% but the CONTAINS one could use another format than %foo% ?

That's why I think we should deprecate the format option and remove it in the next major.

Changelog

### Deprecated
- `format` option of the `StringFilter`.

[phansys]

Why would these checks be made with %foo and foo% but the CONTAINS one could use another format than %foo% ?

I still see the single character mask as a valid use for this option. By instance LIKE f_o. Depending on the engine, I think the LIKE syntax is able to support even more masks than % or _.

[VincentLanglet]

Why would these checks be made with %foo and foo% but the CONTAINS one could use another format than %foo% ?

I still see the single character mask as a valid use for this option. By instance LIKE f_o. Depending on the engine, I think the LIKE syntax is able to support even more masks than % or _.

I didn't know there is others mask. Maybe it's a use case but you will have
Contains -> _foo_
Start-> foo%
End -> %foo
This is not consistent. A mask option could be better to change % to _.
Contains -> _foo_
Start-> foo_
End -> _foo
But do you have a use case ?

There shouldn't be multiple way to contain something or start with something.
If you have a special rule, it would be better to have a special filter.

[phansys]

It's enough for me. Just pointing that MSSQL has support for other masks.

[VincentLanglet]

Done @phansys