Add manual approval support

[dalen]

Hi, this bot looks really nice. But would it be possible to add support for manual approval actions to it? Something like this example, but all built into one bot.

https://aws.amazon.com/blogs/devops/use-slack-chatops-to-deploy-your-code-how-to-integrate-your-pipeline-in-aws-codepipeline-with-your-slack-channel/

[ogrodnek]

Hi @dalen . That sounds great, thanks for the suggestion. I'll look into adding it. If someone wants to submit a PR I'd be happy to include it as well.