feat: Allow excluding the Github Actor from the message

[ondrosh]

Issue

There is currently no way to exclude the Github Actor from being in the message.

Solution

According to the Slack API documentation, the author_link and author_icon values only work if author_name is present.

With omitempty specified on the author_name within the Attachment structure, allowing SLACK_MSG_AUTHOR to be an empty string will result in this field being unset which will allow users to choose if they want to exclude the Github Actor from being in the message.

Changes

• Update main.sh to use = instead of :- on setting the GITHUB_ACTOR which avoids empty strings being substituted
• Update README.md with details on how to avoid including the Github Actor in the message

[shvixxl]

Actually, I have successfully excluded it from the message by using ' ' as a value for SLACK_MSG_AUTHOR

[alexanderkranga]

Thanks @lazy-octopus-kebab , this works as a workaround:

env:
  SLACK_MSG_AUTHOR: ' '

But merging this PR would definitely help us too!