Create CHANGELOG.md for easier communication of library changes, especially possible breaking changes.

Signed-off-by: Owen Williams <owen.williams@grafana.com>

Author: ywwg

CHANGELOG.md

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+# Changelog
+
+## main / unreleased
+
+## What's Changed
+
+* [ENHANCEMENT] Create CHANGELOG.md for easier communication of library changes, especially possible breaking changes.
+
+## v0.66.0 / 2025-09-02
+
+### ⚠️ Breaking Changes ⚠️
+
+* A default-constructed TextParser will be invalid. It must have a valid `scheme` set, so users should use the NewTextParser function to create a valid TextParser. Otherwise parsing will panic with "Invalid name validation scheme requested: unset".
+
+### What's Changed
+* model: add constants for type and unit labels. by @bwplotka in https://github.com/prometheus/common/pull/801
+* model.ValidationScheme: Support encoding as YAML by @aknuds1 in https://github.com/prometheus/common/pull/799
+* fix(promslog): always print time.Duration values as go duration strings by @tjhop in https://github.com/prometheus/common/pull/798
+* Add `ValidationScheme` methods `IsValidMetricName` and `IsValidLabelName` by @aknuds1 in https://github.com/prometheus/common/pull/806
+* Fix delimited proto not escaped correctly by @thampiotr in https://github.com/prometheus/common/pull/809
+* Decoder: Remove use of global name validation and add validation by @ywwg in https://github.com/prometheus/common/pull/808
+* ValidationScheme implements pflag.Value and json.Marshaler/Unmarshaler interfaces by @juliusmh in https://github.com/prometheus/common/pull/807
+* expfmt: Add NewTextParser function by @aknuds1 in https://github.com/prometheus/common/pull/816
+
+* Enable the godot linter by @aknuds1 in https://github.com/prometheus/common/pull/821
+* Enable usestdlibvars linter by @aknuds1 in https://github.com/prometheus/common/pull/820
+* Enable unconvert linter by @aknuds1 in https://github.com/prometheus/common/pull/819
+* Enable the fatcontext linter by @aknuds1 in https://github.com/prometheus/common/pull/822
+* Enable gocritic linter by @aknuds1 in https://github.com/prometheus/common/pull/818
+* Use go.uber.org/atomic instead of sync/atomic by @aknuds1 in https://github.com/prometheus/common/pull/825
+* Enable revive rule unused-parameter by @aknuds1 in https://github.com/prometheus/common/pull/824
+* Enable revive rules by @aknuds1 in https://github.com/prometheus/common/pull/823
+* Synchronize common files from prometheus/prometheus by @prombot in https://github.com/prometheus/common/pull/802
+* Synchronize common files from prometheus/prometheus by @prombot in https://github.com/prometheus/common/pull/803
+* Sync .golangci.yml with prometheus/prometheus by @aknuds1 in https://github.com/prometheus/common/pull/817
+* ci: update upload-actions by @ywwg in https://github.com/prometheus/common/pull/814
+* docs: fix typo in expfmt.Negotiate by @wmcram in https://github.com/prometheus/common/pull/813
+* build(deps): bump golang.org/x/net from 0.40.0 to 0.41.0 by @dependabot[bot] in https://github.com/prometheus/common/pull/800
+* build(deps): bump golang.org/x/net from 0.41.0 to 0.42.0 by @dependabot[bot] in https://github.com/prometheus/common/pull/810
+* build(deps): bump github.com/stretchr/testify from 1.10.0 to 1.11.1 in /assets by @dependabot[bot] in https://github.com/prometheus/common/pull/826
+* build(deps): bump google.golang.org/protobuf from 1.36.6 to 1.36.8 by @dependabot[bot] in https://github.com/prometheus/common/pull/830
+* build(deps): bump golang.org/x/net from 0.42.0 to 0.43.0 by @dependabot[bot] in https://github.com/prometheus/common/pull/829
+* build(deps): bump github.com/stretchr/testify from 1.10.0 to 1.11.1 by @dependabot[bot] in https://github.com/prometheus/common/pull/827
+
+### New Contributors
+* @aknuds1 made their first contribution in https://github.com/prometheus/common/pull/799
+* @thampiotr made their first contribution in https://github.com/prometheus/common/pull/809
+* @wmcram made their first contribution in https://github.com/prometheus/common/pull/813
+* @juliusmh made their first contribution in https://github.com/prometheus/common/pull/807
+