chore: Swapping main superset images for more current versions

[rusackas]

SUMMARY

This just swaps out a few of the Supserset screenshots on the home page at https://superset.apache.org/. I tried to find decent shots of stock dashboards. They might not be the most whiz-bang examples, but are SO much more current, so the UI looks fresh.

More updates to the home page will probably follow over time... trying to keep things bite size!

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

cd docs
yarn install  # Installs NPM dependencies
yarn start  # Starts development server at http://localhost:3000

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 #22668 (bc22f1d) into master (73e53fa) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #22668   +/-   ##
=======================================
  Coverage   67.10%   67.10%           
=======================================
  Files        1869     1869           
  Lines       71580    71580           
  Branches     7806     7806           
=======================================
  Hits        48031    48031           
  Misses      21521    21521           
  Partials     2028     2028           

Flag	Coverage Δ
hive	52.60% <ø> (ø)
javascript	53.96% <ø> (ø)
mysql	78.01% <ø> (ø)
postgres	78.08% <ø> (ø)
presto	52.49% <ø> (ø)
python	81.31% <ø> (ø)
sqlite	76.48% <ø> (ø)
unit	51.47% <ø> (ø)

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[villebro]

Looks much better!