Add owner and parent fields clarification to docs (#35023)

Issue: https://github.com/go-gitea/gitea/issues/9637

Changes introduced: I have clarified the problematic terms (owner and
parent) in all affected endpoints.

The changes were made to relevant:

- HTTP endpoint parameters' descriptions
- response/request models' fields

This MR is big, but most changes are the same. If you'd like me to break
this MR into several smaller ones, let me know :)

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/structs/issue.go

@@ -262,7 +262,8 @@ func (it IssueTemplate) Type() IssueTemplateType {
 // IssueMeta basic issue information
 // swagger:model
 type IssueMeta struct {
-	Index int64  `json:"index"`
+	Index int64 `json:"index"`
+	// owner of the issue's repo
 	Owner string `json:"owner"`
 	Name  string `json:"repo"`
 }