[feature] Enable snapshot images in Slack notifications

[jonfairbanks]

Version and OS
v0.49.4 on Docker

Is your feature request related to a problem? Please describe.
I currently have ChangeDetection integrated with Browserless for taking snapshots of websites to detect changes. I also have a notification integration with Slack and have toggled the Attach screenshot to notification option.

Unfortunately, when notifications come into Slack, they do not contain a screenshot. The Slack API does support attachments in messages posted via their API however.

Describe the solution you'd like
When a change is detected and Slack is notified, a snapshot is shared in the Slack message body.

Describe the use-case and give concrete real-world examples
Notification body:

There's a new update available!

{{watch_url}}

If any additional details or examples are needed, please let me know!

[dgtlmoon]

Hmm where in the API docs does slack say it supports images on the message? https://api.slack.com/methods/chat.postMessage

[dgtlmoon]

it looks like theres two ways

• slack doesnt support adding an image with a message, BUT you can link to some external image URL
• slack will let you upload a file, get the file URL, and then link the file (using the file URL) from a slack message

i dont think this is supported in caronc/apprise

[jonfairbanks]

Yea, these would probably have to go as a file.upload with an included comment.

https://api.slack.com/methods/files.upload/code

[dgtlmoon]

Any chance you can add me to your slack? it looks like apprise does actually support it when in self.mode is SlackMode.BOT:

https://github.com/caronc/apprise/blob/efd9d5cd676304a198d3d993ee1face8b7f6d55c/apprise/plugins/slack.py#L644-L680