docs: clarify YAML quoting vs matcher token quoting

[Cloud-Architect-Emma]

Fixes #5099

Adds a note under the "UTF-8 matchers" section clarifying the distinction between YAML quoting and matcher token quoting.

Problem: The documentation describes double-quoting of individual matcher tokens (label name, label value) but does not explain that this quoting is handled by Alertmanager's own parser, not by YAML. Users writing env =~ "prod" without surrounding YAML quotes may believe the inner double quotes protect against YAML special characters, which they do not.

Change: Added a blockquote note explaining the three YAML quoting styles (plain, single-quoted, double-quoted) with examples, and explicitly clarifying that inner double quotes on matcher tokens provide no YAML-level protection.

Summary by CodeRabbit

• Documentation
  • Expanded configuration documentation with detailed clarification on YAML quoting behavior and its relationship to Alertmanager matcher token parsing. Added comprehensive guidance on appropriate use of plain, single-quoted, and double-quoted YAML scalar formats, including important warnings about protecting configuration values against YAML special characters.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: affaa305-aff7-41ed-a921-a2a0ec8ec227

📥 Commits

Reviewing files that changed from the base of the PR and between 45996cb and b827e4f.

📒 Files selected for processing (1)

• docs/configuration.md

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📝 Walkthrough

Walkthrough

Documentation note added to clarify that YAML quoting rules apply to entire matcher strings, not individual tokens. Examples demonstrate plain-style, single-quoted, and double-quoted YAML scalar approaches for matcher entries.

Changes

Matcher YAML Quoting Documentation

Layer / File(s)	Summary
YAML quoting vs. matcher token quoting note docs/configuration.md	Added clarification explaining how YAML quoting applies to the whole matcher string and providing examples for plain, single-quoted, and double-quoted YAML styles, with guidance on when each is appropriate.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: documentation clarification about YAML quoting versus matcher token quoting.
Description check	✅ Passed	The description provides clear context about the issue being fixed, the problem identified, and the specific changes made to address it.
Linked Issues check	✅ Passed	The PR directly addresses issue #5099 by adding documentation that clarifies YAML quoting styles and explains that inner double quotes on matcher tokens do not provide YAML-level protection.
Out of Scope Changes check	✅ Passed	The changes are limited to documentation updates in docs/configuration.md related to the matcher quoting clarification, with no out-of-scope alterations.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[Cloud-Architect-Emma]

Hi maintainers, could someone please approve the workflow run so the build and test checks can execute? This is a

documentation-only change adding a note to clarify YAML quoting vs matcher token quoting as reported in #5099. DCO is passing.

Thanks!