API Generalize Header for get XY list endpoints

[6543]

as title, if an api endpoint returns a list of objects it should:
A: support paggination (optional)
B: add max-obj-count to header

• add this to API programming guidelinge

• create header for all get list endpints

• ctx.Header().Set("X-Total-Count", fmt.Sprintf("%d", maxResults))

[zeripath]

I would be cautious about assuming that we should always provide a full count - that can be very expensive in certain circumstances - (mostly circumstances that we've already committed to providing a count.)

[6543]

good point ...

[6543]

... maybe it's better to add a help function named as ctx.SetResultHeader(...) to do it.

Originally posted by @a1012112796 in #16300 (comment)