fix: accept only JSON credentials

[betodealmeida]

SUMMARY

In the file dialog for selecting credentials for BigQuery, allow only JSON files to be selected.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before:

After is the same, but only JSON files can be selected. :)

TESTING INSTRUCTIONS

1. Add Biguery DB, click file upload button.

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 #22040 (45f51bb) into master (9832bbd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #22040   +/-   ##
=======================================
  Coverage   67.00%   67.00%           
=======================================
  Files        1815     1815           
  Lines       69540    69540           
  Branches     7483     7483           
=======================================
  Hits        46592    46592           
  Misses      21017    21017           
  Partials     1931     1931           

Flag	Coverage Δ
javascript	53.45% <ø> (ø)

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

Impacted Files	Coverage Δ
...aseModal/DatabaseConnectionForm/EncryptedField.tsx	10.00% <ø> (ø)

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[Antonio-RiveroMartnez]

LGTM!

[lyndsiWilliams]

I pulled this down locally to test it out, it works! LGTM 😁