Argument to perform send-notifications

[timkrins]

Aims to solve #1436

TODO:

• Tests
• Check arguments (documentation at https://docs.codecov.com/docs/cli-options#send-notifications des not list any, but I want to confirm that - for now I have copied most arguments from the other commands).

[thomasrockhu-codecov]

Sorry for the delay here, @timkrins. We decided to go a more generic route and you can supply those args along with the command as run_command

[timkrins]

No problem at all