built-in function: Support degrees() function

[jingchen2222]

Is your feature request related to a problem? Please describe.

degrees(value) - Converts radians to degrees.

Examples:

SELECT degrees(3.141592653589793);
-- output  180.0

reference:
https://dev.mysql.com/doc/refman/8.0/en/mathematical-functions.html#function_degrees
https://spark.apache.org/docs/2.3.0/api/sql/#degrees

Describe the solution you'd like

We do provide a built-in function development guide for you.
Please check OpenMLDB Build-In Function Develop Guide or the Chinese version for help.

Please make sure you:

• Add built-in C++ function in src/udf/udf.h and src/udf/udf.cc
• Register function to default library from function void DefaultUdfLibrary::IniMathUdf() in src/udf/default_udf_library.cc.
• Add related unit test in src/codegen/udf_ir_builder_test.cc
• Documenting function

If you have any questions or concerns, please let us know. We appreciate every piece of code, comment.
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[wuxiaobai24]

I would like to help