Adding Slack notifications for e2e tests

[eviltwinhans]

Action used: https://github.com/marketplace/actions/slack-github-actions-slack-integration
Secret added: SLACK_WEBHOOK_URL

[codecov]

Codecov Report

Merging #2804 (9c182be) into master (d61909e) will decrease coverage by 11.42%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #2804       +/-   ##
===========================================
- Coverage   84.65%   73.22%   -11.43%     
===========================================
  Files          72       70        -2     
  Lines       12429    12196      -233     
  Branches     2123     2100       -23     
===========================================
- Hits        10522     8931     -1591     
- Misses       1493     2959     +1466     
+ Partials      414      306      -108     

Impacted Files	Coverage Δ
neuro-cli/src/neuro_cli/storage.py	34.22% <0.00%> (-46.14%)	⬇️
neuro-cli/src/neuro_cli/disks.py	51.35% <0.00%> (-40.55%)	⬇️
neuro-cli/src/neuro_cli/job.py	43.35% <0.00%> (-37.11%)	⬇️
neuro-cli/src/neuro_cli/image.py	40.00% <0.00%> (-34.82%)	⬇️
neuro-cli/src/neuro_cli/ael.py	16.30% <0.00%> (-33.34%)	⬇️
neuro-sdk/src/neuro_sdk/_buckets.py	54.59% <0.00%> (-31.09%)	⬇️
neuro-cli/src/neuro_cli/secrets.py	61.53% <0.00%> (-26.93%)	⬇️
neuro-cli/src/neuro_cli/root.py	70.52% <0.00%> (-24.22%)	⬇️
neuro-sdk/src/neuro_sdk/_bucket_base.py	63.12% <0.00%> (-23.13%)	⬇️
neuro-cli/src/neuro_cli/blob_storage.py	37.56% <0.00%> (-22.49%)	⬇️
... and 35 more

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