[outcome] Add option single_header

[jeremy-coulon]

Summary

Changes to recipe: outcome/*

Motivation

Add single_header option. Default is True for backward compatibility.

Details

I need single_header=False for my own recipe of LLFIO
I found a duplicate PR which is closed here #15995
My solution seems much simpler.

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• Read the contributing guidelines
• Checked that this PR is not a duplicate: list of PRs by recipe
• Tested locally with at least one configuration using a recent version of Conan

[jeremy-coulon]

outcome also depends on a recent version of status-code when single_header=False

Waiting for this PR to be merged: #24728

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 4 (641357f16dcea7b71c05551065879276ee209a1a):

• outcome/2.2.8:
  All packages built successfully! (All logs)

• outcome/2.2.9:
  All packages built successfully! (All logs)

• outcome/2.2.7:
  All packages built successfully! (All logs)

• outcome/2.2.4:
  All packages built successfully! (All logs)

• outcome/2.1.5:
  All packages built successfully! (All logs)

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Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 4 (641357f16dcea7b71c05551065879276ee209a1a):

• outcome/2.2.8:
  All packages built successfully! (All logs)

• outcome/2.2.9:
  All packages built successfully! (All logs)

• outcome/2.2.7:
  All packages built successfully! (All logs)

• outcome/2.2.4:
  All packages built successfully! (All logs)

• outcome/2.1.5:
  All packages built successfully! (All logs)