Enable markdownlint no-trailing-punctuation and no-blanks-blockquote (#29214)

Enable these two and fix issues.

docs/content/administration/customizing-gitea.en-us.md

@@ -284,7 +284,7 @@ syntax and shouldn't be touched without fully understanding these components.
 
 Google Analytics, Matomo (previously Piwik), and other analytics services can be added to Gitea. To add the tracking code, refer to the `Other additions to the page` section of this document, and add the JavaScript to the `$GITEA_CUSTOM/templates/custom/header.tmpl` file.
 
-## Customizing gitignores, labels, licenses, locales, and readmes.
+## Customizing gitignores, labels, licenses, locales, and readmes
 
 Place custom files in corresponding sub-folder under `custom/options`.
 

docs/content/administration/mail-templates.en-us.md

@@ -222,7 +222,7 @@ Please check [Gitea's logs](administration/logging-config.md) for error messages
         <a href="{{.Link}}">{{.Repo}}#{{.Issue.Index}}</a>.
         </p>
         {{if not (eq .Body "")}}
-            <h3>Message content:</h3>
+            <h3>Message content</h3>
             <hr>
             {{.Body | Str2html}}
         {{end}}
@@ -245,7 +245,7 @@ This template produces something along these lines:
 
 > [@rhonda](#) (Rhonda Myers) updated [mike/stuff#38](#).
 >
-> #### Message content:
+> #### Message content
 >
 > \_********************************\_********************************
 >

docs/content/administration/mail-templates.zh-cn.md

@@ -228,7 +228,7 @@ _主题_ 和 _邮件正文_ 由 [Golang的模板引擎](https://go.dev/pkg/text/
 
 > [@rhonda](#)（Rhonda Myers）更新了 [mike/stuff#38](#)。
 >
-> #### 消息内容：
+> #### 消息内容
 >
 > \_********************************\_********************************
 >