feat: Route --version output to stdout

[neo-anderson]

Currently, saml2aws --version prints the application version to stderr. This change modifies the behavior to print the version string to stdout instead while other logs and errors remain on stderr.

Reasoning:

Printing the version to stdout aligns better with common scripting practices and standard CLI tool behavior for version reporting. This makes it easier to capture the version string programmatically without needing stderr redirection (2>&1).

For example, users with bootstrapping or environment setup scripts that check dependency versions currently need to add special handling for saml2aws like

version = result.stdout.strip() if tool != "saml2aws" else result.stderr.strip()

or like

VERSION=$(saml2aws --version 2>&1)

Routing --version output to stdout removes this inconsistency.

https://github.com/Versent/saml2aws/issues/1432

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 28.14%. Comparing base (99d6fe4) to head (6e86cdc). Report is 155 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/saml2aws/main.go	0.00%	3 Missing :warning:

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Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1431       +/-   ##
===========================================
- Coverage   42.19%   28.14%   -14.06%     
===========================================
  Files          54       70       +16     
  Lines        6456    12540     +6084     
===========================================
+ Hits         2724     3529      +805     
- Misses       3283     8535     +5252     
- Partials      449      476       +27     

Flag	Coverage Δ
unittests	28.14% <0.00%> (-14.06%)	:arrow_down:

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[neo-anderson]

Instead of reimplementing the Version() function it looks like we can set the usage and version output to write with os.stdout using .UsageWriter().

So we keep the .Version( and we set the .UsageWriter(. I've checked, but we should verify, this should not interfere with error messages caused by incorrect commands from going to stderr because that is handled by fatalUsage().

https://github.com/alecthomas/kingpin/blob/64d23c54e3e2a385ce12757939bed9c632d1693c/app.go#L146

Thanks for the review. That's way cleaner.

[neo-anderson]

I verified that errors are sent to stderr by running this: $GOPATH/bin/saml2aws invalid 1>out.txt 2>err.txt