Add project name and environment to slack notification

[kostek-pl]

Is your feature request related to a problem? Please describe.
Currently slack notification title looks like this:

If there are many dbt projects and environments we need to create lot of separate slack channels to distinguish from which dbt project and environment monitoring summary comes from.

Describe the solution you'd like
To make it easier and more convenient we should add project name and environment to the header so it could look like:

• when --project-name is not provided
  

• when --project-name is provided()
  

Would you be willing to contribute this feature?
Yes, i will contribute and take care of this

[haritamar]

Hi @kostek-pl !
Following up on this issue - thanks a lot for opening a PR.
I've noticed that @ellakz left a couple of comments, if you can take a look would be great, then we can ensure this gets into the next version.