[chore]: Bump github.com/prometheus/client_golang from 1.20.5 to 1.21.0 (#3860)

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 1.20.5 to 1.21.0.
- [Release notes](https://github.com/prometheus/client_golang/releases)
- [Changelog](https://github.com/prometheus/client_golang/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prometheus/client_golang/compare/v1.20.5...v1.21.0)

---
updated-dependencies:
- dependency-name: github.com/prometheus/client_golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

vendor/github.com/prometheus/common/model/metric.go

@@ -28,13 +28,13 @@ import (
 
 var (
 	// NameValidationScheme determines the method of name validation to be used by
-	// all calls to IsValidMetricName() and LabelName IsValid(). Setting UTF-8 mode
-	// in isolation from other components that don't support UTF-8 may result in
-	// bugs or other undefined behavior. This value is intended to be set by
-	// UTF-8-aware binaries as part of their startup. To avoid need for locking,
-	// this value should be set once, ideally in an init(), before multiple
-	// goroutines are started.
-	NameValidationScheme = LegacyValidation
+	// all calls to IsValidMetricName() and LabelName IsValid(). Setting UTF-8
+	// mode in isolation from other components that don't support UTF-8 may result
+	// in bugs or other undefined behavior. This value can be set to
+	// LegacyValidation during startup if a binary is not UTF-8-aware binaries. To
+	// avoid need for locking, this value should be set once, ideally in an
+	// init(), before multiple goroutines are started.
+	NameValidationScheme = UTF8Validation
 
 	// NameEscapingScheme defines the default way that names will be escaped when
 	// presented to systems that do not support UTF-8 names. If the Content-Type