feat(csv-upload): Configurable max filesize

[giftig]

SUMMARY

Add a validation utility to validate maximum file size when uploading CSVs, and install it on the CsvToDatabaseForm, backed by an optional parameter in application config.

TESTING INSTRUCTIONS

1. Configure a maximum upload size
2. Attempt to upload files of varying sizes

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

[giftig]

I got an error while trying to unit test this locally; not sure if there's a bug on the master branch at the moment or if I had an issue with my dependencies, so I've opened the PR a tad early to get a CI build running on it.

[codecov]

Codecov Report

Merging #24618 (c7f32b8) into master (c53b249) will decrease coverage by 0.56%.
The diff coverage is 100.00%.

❗ Current head c7f32b8 differs from pull request most recent head 1f2e815. Consider uploading reports for the commit 1f2e815 to get more accurate results

@@            Coverage Diff             @@
##           master   #24618      +/-   ##
==========================================
- Coverage   68.97%   68.42%   -0.56%     
==========================================
  Files        1907     1907              
  Lines       74153    74166      +13     
  Branches     8182     8182              
==========================================
- Hits        51148    50749     -399     
- Misses      20882    21294     +412     
  Partials     2123     2123              

Flag	Coverage Δ
hive	54.14% <57.14%> (?)
postgres	?
presto	54.04% <57.14%> (-0.01%)	⬇️
python	82.17% <100.00%> (-1.16%)	⬇️
sqlite	78.12% <71.42%> (-0.01%)	⬇️
unit	54.84% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
superset/views/database/forms.py	93.67% <ø> (ø)
superset/config.py	92.17% <100.00%> (+0.02%)	⬆️
superset/forms.py	97.72% <100.00%> (+0.85%)	⬆️

... and 37 files with indirect coverage changes

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[rusackas]

LGTM, but leaving it open for additional opinions.

[villebro]

Looks great!

[giftig]

Looks like the only failure is in the postgres integration tests and that looks like a flaky test ("now" != "a second ago" is very suspicious as test failures go). I've just pushed a rebase anyway so hopefully the next run is successful.