Extended the hook_url functionality to Slack

[muffato]

Hello,

Got very interested in what @matthdsm did in #1798 . This is a small extension to support Slack as well, since Slack doesn't understand adaptive cards.

Here is how the notifications look like:

The JSON has a very long and tricky line where I try to improve the look-and-feel of the pipeline configuration:

• paths are printed as code
• dates are formatted according to the locale settings
• the hook_url itself is hidden

Note: I am using the legacy "attachments" method of the Slack API, rather than the now-recommended Block Kit method, because I couldn't find how to make the latter put some colour. I think one has to immediately know whether it failed or not, and the colour is faster to recognise than the text itself.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #1829 (33a09af) into dev (7010335) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1829   +/-   ##
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  Coverage   63.74%   63.74%           
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  Files          41       41           
  Lines        4913     4913           
=======================================
  Hits         3132     3132           
  Misses       1781     1781           

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[matthdsm]

Love it, just left one small comment

[muffato]

IM_notification can do. I feel uninspired today and can't find a better name

[muffato]

Is this considered to be superseded by https://github.com/Midnighter/nf-slack ?

[muffato]

Thank you !

[mashehu]

Please add documentation about this nf-core/website#1455