feat: support display private key discreetly

[Halimao]

Motivation

close #10016

When we run leo account new or leo account import, will display private key discreently on an alternate screen. See following pics

[ghost]

This issue does not qualify for a contributor badge because a bot is suspected. If you are not a bot, please reach out to us directly and provide proof.

[Halimao]

This issue does not qualify for a contributor badge because a bot is suspected. If you are not a bot, please reach out to us directly and provide proof.

This doesn't for the contributor badge, but add a new feature to leo.

[Halimao]

@d0cd Sincerely thanks😀

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (6126189) 79.53% compared to head (f354221) 76.28%.
Report is 221 commits behind head on testnet3.

Files	Patch %	Lines
leo/cli/commands/account.rs	0.00%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           testnet3   #10018      +/-   ##
============================================
- Coverage     79.53%   76.28%   -3.26%     
============================================
  Files           172      200      +28     
  Lines          5776     6759     +983     
  Branches       5776     6759     +983     
============================================
+ Hits           4594     5156     +562     
- Misses         1182     1603     +421     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Halimao]

@d0cd Hi sir, can we get this merged, IMO this pr won't affect the current flow of leo account new|import, there is a new flag --discreet to use the feature of this pr

[d0cd]

Left some minor nits but looks good overall!
Thank you for contributing! 🚀