Add description in CRD definition to explain returnCopy and maxData fields

[mtardy]

We can also enrich the TracingPolicy reference on the same occasion.

For maxData we can use what was written in TracingPolicy reference:

description: Read maximum possible data (currently 327360). This field is only used for char_buff data. When this value is false (default), the bpf program will fetch at most 4096 bytes. In later kernels (>=5.4) tetragon supports fetching up to 327360 bytes if this flag is turned on.

It feels like it could be a good idea to generate TracingPolicy docs straight from the CRD definition as well. Rewriting the description for all the args types and all the fields description seems redundant.