Modify the content format of the Feishu webhook (#25106)

close https://github.com/go-gitea/gitea/issues/24368

## what my pull request does

Since the official documentation states that custom bots do not support
hyperlink functionality, simply adding it without making some formatting
changes would result in an unappealing output. Therefore, I have
modified the formatting of the output. Currently, it is only used for
Feishu.

--- 


[docs](https://open.feishu.cn/document/uAjLw4CM/ukTMukTMukTM/im-v1/message/create_json#%E8%B6%85%E9%93%BE%E6%8E%A5%E4%BD%BF%E7%94%A8%E8%AF%B4%E6%98%8E)

<img width="641" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/360e1c81-ab64-4ef6-851e-aa450d6e85a4">

- Issue

<img width="423" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/519f6fae-81ab-4ec8-89b8-f6a73ff93783">


- Issue Comment


<img width="548" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/749c0d1c-3657-431e-b787-8bf4c23cce83">


- Assign

<img width="431" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/066f99e5-eabb-455d-91fb-a8359cc26dc7">

<img width="457" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/c6c10f99-db83-46ef-a775-4c91979fa68f">

- Merge

<img width="408" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/e627bf43-5954-45aa-acf6-261ee046802f">

- PullRequest

<img width="425" alt="image"
src="https://github.com/go-gitea/gitea/assets/75628309/72cfa714-d3fa-4fb9-abdd-e8508d756056">

services/webhook/general_test.go

@@ -123,6 +123,10 @@ func issueTestPayload() *api.IssuePayload {
 			HTMLURL: "http://localhost:3000/test/repo/issues/2",
 			Title:   "crash",
 			Body:    "issue body",
+			Poster: &api.User{
+				UserName:  "user1",
+				AvatarURL: "http://localhost:3000/user1/avatar",
+			},
 			Assignees: []*api.User{
 				{
 					UserName:  "user1",
@@ -161,7 +165,11 @@ func issueCommentTestPayload() *api.IssueCommentPayload {
 			URL:     "http://localhost:3000/api/v1/repos/test/repo/issues/2",
 			HTMLURL: "http://localhost:3000/test/repo/issues/2",
 			Title:   "crash",
-			Body:    "this happened",
+			Poster: &api.User{
+				UserName:  "user1",
+				AvatarURL: "http://localhost:3000/user1/avatar",
+			},
+			Body: "this happened",
 		},
 	}
 }
@@ -190,6 +198,10 @@ func pullRequestCommentTestPayload() *api.IssueCommentPayload {
 			HTMLURL: "http://localhost:3000/test/repo/pulls/12",
 			Title:   "Fix bug",
 			Body:    "fixes bug #2",
+			Poster: &api.User{
+				UserName:  "user1",
+				AvatarURL: "http://localhost:3000/user1/avatar",
+			},
 		},
 		IsPull: true,
 	}
@@ -254,6 +266,10 @@ func pullRequestTestPayload() *api.PullRequestPayload {
 			Title:     "Fix bug",
 			Body:      "fixes bug #2",
 			Mergeable: true,
+			Poster: &api.User{
+				UserName:  "user1",
+				AvatarURL: "http://localhost:3000/user1/avatar",
+			},
 			Assignees: []*api.User{
 				{
 					UserName:  "user1",