doc(udf): merge udf docs for the same function

some UDFs may has mutiple doc string, each for different parameters type. The problem is for udf doc gen, it is unclear which doc string to publish in the generated doc (as the document only has one entry for each, it selects random one). Refer the PR #2734 .

know problem udfs

• ilike_match
• like_match
• regexp_like
• string
• substring
• or anything else you find

Solution

merge the multiple doc strings into single one, with all informations included. See how dayofyear implemented: https://github.com/4paradigm/OpenMLDB/blob/c1d5e1d4e810590e678d77294774832f0ad1a394/hybridse/src/udf/default_udf_library.cc#L2178-L2210