Support sending notification to DingTalk

[wanjunlei]

The purpose of this pr is to enable alertmanager to send notifications to DingTalk Chatbot. For this purpose, i create a new Notifier and a new config. It is a example of the dingtalk receiver config.

receivers:
- name: 'dingtalk'
  dingtalk_configs:
  - webhook: 'https://oapi.dingtalk.com/robot/send?access_token=365199e133d8f08a1e3bc70e3803b3b4f129ad381c5297d5caf676a3'
    keywords:
    - 'alertmanager'
    secret: 'SECf2b1928e08f9f38c202a369edcb7ea295132424a8109c21dc604e70935'

The test result is as follows.

[simonpasquier]

Thanks for suggesting this change. Unfortunately, we are currently not accepting new integrations.

We can only provide the stability and performance we want to provide if we can properly maintain the codebase. This includes, amongst others, test integrations in an automated and scalable fashion. For this reason, we are suggesting people integrate with the help of our generic webhook interface (note that there's already a DingTalk integration listed here).

[jeyrce]

@simonpasquier In fact dingtalk is a verify popular im tool for orgization in China, the same as wechat, and will be more international in the future. So it's a good idea to add dingtalk_configs for alertmanager as a built-in notification way.

[alswl]

Duplicated with #1276

[SoloJacobs]

Hi,

We've recently decided that the Alertmanager project will now be accepting PRs for new integrations. This opens the door for your previous contribution. Are you interested in resurrecting this PR?

If you are interested in moving forward, here are the requirements:

• The PR must be rebased against main.
• All CI checks must pass successfully.
• The implementation needs decent test coverage.
• Please link the API references that are used during development, both in the PR and the code itself.

We also expect you to spend some time providing community support by answering questions about issues opened by users relating to your integration. In return, I commit to providing speedy reviews and will advocate for the inclusion of your PRs.

Thank you very much for your time and potential contribution!

Kind regards, Solomon Jacobs