Add webhook payload size optimization options

[kerwin612]

This PR adds webhook payload size optimization options to help reduce payload size for large commits or pushes with many commits. This feature is particularly useful for target URLs that restrict payload size or have performance problems handling large JSON parsing.

[wxiaoguang]

It should be more flexible to use "limit number" instead of "bool"

[kerwin612]

It should be more flexible to use "limit number" instead of "bool"

Is this OK?

[wxiaoguang]

1. IIRC all other places use "-1" for "no-limit" when "0" is used for "limit to zero".
   • For example: the limit of the repo number
2. Maybe we need a JSON column but not many new separate columns.
3. There are some issues asking about "commit order", so some users want the first N commits, while some other users want the last N commits
   • Use forward order for commits in webhook notifications #21313
   • Don't reverse order of commits in webhooks #21252

[kerwin612]

[wxiaoguang]

The logic is almost the same as the code touched in "Add toggleClass function in dom.ts (#34063)": use checkbox or radio input to toggle some elements, enable some while disable others .

[wxiaoguang]

All pointers can be replaced by the struct, then no need to do any nil check.

And, JSON default values work this way:

s := SomeStruct{ default values }
json.Unmarshal(str, &s)
// then s still keeps the default values if there is no related key in the JSON str

[wxiaoguang]

Optimization reads strange. Optimization means "improve something while keep the result the same as before"

Here it is likely just a "config" system.