chore(stdout) ensure stdout and stderr are not terminals

[sthaha]

Previously when stdout exporter is enabled, it writes to stdout (by default) and logs get written to stderr. This messes up the output. This PR ensures that when stdout exporter is enabled, and log (stderr) isn't redirected, the application quits.

sudo ./bin/kepler --exporter.stdout 

time=2025-05-21T08:45:43.484-04:00 level=ERROR source=cmd/kepler/main.go:53 msg="failed to initialize services" error="failed to initialize service stdout: stdout and stderr are both terminal streams; redirect stderr to a file"

sudo ./bin/kepler --exporter.stdout --no-exporter.prometheus 2>/dev/null

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Press Ctrl+C to shutdown
┌─────────┬─────────────┬─────────────┬────────────────┐
│  ZONE   │ DELTA ( W ) │ POWER ( W ) │ ABSOLUTE ( J ) │
├─────────┼─────────────┼─────────────┼────────────────┤
│    core │       0.86J │       0.43W │      33843.02J │
│ package │      20.84J │      10.42W │      64863.30J │
└─────────┴─────────────┴─────────────┴────────────────┘

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.87%. Comparing base (75c6430) to head (8a60485).

Files with missing lines	Patch %	Lines
internal/exporter/stdout/stdout.go	62.50%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           reboot    #2093      +/-   ##
==========================================
- Coverage   92.16%   91.87%   -0.30%     
==========================================
  Files          30       30              
  Lines        2209     2216       +7     
==========================================
  Hits         2036     2036              
- Misses        131      136       +5     
- Partials       42       44       +2     

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[vimalk78]

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