https://developers.dingtalk.com/document/app/message-link-description
To open the link in browser, we should use this URL: `"dingtalk://dingtalkclient/page/link?pc_slide=false&url=" + url.QueryEscape(singleURL)`
Otherwise the page is displayed inside DingTalk client, it makes users very difficult to visit non-public URLs in DingTalk webhook messages.
* Added tests for MS Teams.
* Added tests for Dingtalk.
* Added tests for Telegram.
* Added tests for Feishu.
* Added tests for Discord.
* Added tests for closed issue and pullrequest comment.
* Added tests for Matrix.
* Trim all spaces.
* Added tests for Slack.
* Added JSONPayload tests.
* Added general tests.
* Replaced duplicated code.
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
