chore(slack): use recommended method for file upload

[betodealmeida]

SUMMARY

Use the files_upload_v2 method in the Slack client, instead of files_upload, see this thread.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

Updated integration test.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #23744 (8ef4305) into master (f3f5d92) will increase coverage by 0.00%.
The diff coverage is 98.66%.

❗ Current head 8ef4305 differs from pull request most recent head f712752. Consider uploading reports for the commit f712752 to get more accurate results

@@           Coverage Diff           @@
##           master   #23744   +/-   ##
=======================================
  Coverage   68.17%   68.18%           
=======================================
  Files        1941     1941           
  Lines       75209    75241   +32     
  Branches     8155     8158    +3     
=======================================
+ Hits        51277    51306   +29     
- Misses      21849    21852    +3     
  Partials     2083     2083           

Flag	Coverage Δ
hive	53.17% <99.47%> (+<0.01%)	⬆️
mysql	78.90% <100.00%> (+<0.01%)	⬆️
postgres	78.97% <100.00%> (+<0.01%)	⬆️
presto	53.09% <99.47%> (+<0.01%)	⬆️
python	82.75% <100.00%> (+<0.01%)	⬆️
sqlite	77.50% <100.00%> (+<0.01%)	⬆️
unit	52.98% <99.47%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...chart-echarts/src/MixedTimeseries/controlPanel.tsx	56.52% <ø> (ø)
...hart-echarts/src/MixedTimeseries/transformProps.ts	0.00% <0.00%> (ø)
superset/datasource/api.py	100.00% <ø> (ø)
superset-frontend/src/SqlLab/actions/sqlLab.js	68.53% <100.00%> (+2.19%)	⬆️
superset/advanced_data_type/api.py	100.00% <100.00%> (ø)
superset/annotation_layers/annotations/api.py	89.31% <100.00%> (ø)
superset/annotation_layers/api.py	86.32% <100.00%> (ø)
superset/async_events/api.py	100.00% <100.00%> (ø)
superset/available_domains/api.py	100.00% <100.00%> (ø)
superset/cachekeys/api.py	96.15% <100.00%> (ø)
... and 38 more

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[Antonio-RiveroMartnez]

LGTM!