refactor: Use printer object for output

[TerryHowe]

What this PR does / why we need it:

Change the last calls to fmt.Fprint to use the printer object.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.26%. Comparing base (145ea7a) to head (1bc45dc).

Files	Patch %	Lines
cmd/oras/root/login.go	66.66%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1426      +/-   ##
==========================================
- Coverage   85.32%   85.26%   -0.07%     
==========================================
  Files         106      106              
  Lines        3810     3808       -2     
==========================================
- Hits         3251     3247       -4     
- Misses        334      336       +2     
  Partials      225      225              

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[qweeah]

LGTM, I think we can add a dedicated option to reduce duplicated output.NewPrinter(cmd.OutOrStdout(), opts.Verbose) though

[TerryHowe]

I think we can add a dedicated option to reduce duplicated output.NewPrinter(cmd.OutOrStdout(), opts.Verbose) though

I should probably step back and look at where this has gone. Generally, I'm pretty happy, but I'm sure there is room for improvement somewhere.