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

Enable these two and fix issues.

.markdownlint.yaml

 line-length: {code_blocks: false, tables: false, stern: true, line_length: -1}
 no-alt-text: false
 no-bare-urls: false
-no-blanks-blockquote: false
 no-emphasis-as-heading: false
 no-empty-links: false
 no-hard-tabs: {code_blocks: false}
 no-inline-html: false
 no-space-in-code: false
 no-space-in-emphasis: false
-no-trailing-punctuation: false
 no-trailing-spaces: {br_spaces: 0}
 single-h1: false

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

 
 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

         <a href="{{.Link}}">{{.Repo}}#{{.Issue.Index}}</a>.
         </p>
         {{if not (eq .Body "")}}
-            <h3>Message content:</h3>
+            <h3>Message content</h3>
             <hr>
             {{.Body | Str2html}}
         {{end}}
 
 > [@rhonda](#) (Rhonda Myers) updated [mike/stuff#38](#).
 >
-> #### Message content:
+> #### Message content
 >
 > \_********************************\_********************************
 >

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

 
 > [@rhonda](#)（Rhonda Myers）更新了 [mike/stuff#38](#)。
 >
-> #### 消息内容：
+> #### 消息内容
 >
 > \_********************************\_********************************
 >

docs/content/contributing/guidelines-frontend.en-us.md

 
 We recommend [Google HTML/CSS Style Guide](https://google.github.io/styleguide/htmlcssguide.html) and [Google JavaScript Style Guide](https://google.github.io/styleguide/jsguide.html)
 
-### Gitea specific guidelines:
+### Gitea specific guidelines
 
 1. Every feature (Fomantic-UI/jQuery module) should be put in separate files/directories.
 2. HTML ids and classes should use kebab-case, it's preferred to contain 2-3 feature related keywords.

docs/content/contributing/guidelines-frontend.zh-cn.md

 
 我们推荐使用[Google HTML/CSS Style Guide](https://google.github.io/styleguide/htmlcssguide.html)和[Google JavaScript Style Guide](https://google.github.io/styleguide/jsguide.html)。
 
-## Gitea 特定准则：
+## Gitea 特定准则
 
 1. 每个功能（Fomantic-UI/jQuery 模块）应放在单独的文件/目录中。
 2. HTML 的 id 和 class 应使用 kebab-case，最好包含2-3个与功能相关的关键词。

docs/content/development/api-usage.zh-cn.md

 `/users/:name/tokens` 是一个特殊的接口，需要您使用 basic authentication 进行认证，具体原因在 issue 中
 [#3842](https://github.com/go-gitea/gitea/issues/3842#issuecomment-397743346) 有所提及，使用方法如下所示：
 
-### 使用 Basic authentication 认证：
+### 使用 Basic authentication 认证
 
 ```
 $ curl --url https://yourusername:yourpassword@gitea.your.host/api/v1/users/yourusername/tokens