Prepare v0.66.0 release (#6834)

Signed-off-by: Johan Fylling <johan.dev@fylling.se>

CHANGELOG.md

@@ -3,7 +3,83 @@
 All notable changes to this project will be documented in this file. This
 project adheres to [Semantic Versioning](http://semver.org/).
 
-## Unreleased
+## 0.66.0
+
+This release contains a mix of features, performance improvements, and bugfixes.
+
+### Improved Test Reports ([2546](https://github.com/open-policy-agent/opa/issues/2546))
+
+The `opa test` command now includes a new `--var-values` flag that enriches reporting of failed tests with the values and locations for variables in the failing expression.
+E.g.:
+
+```
+FAILURES
+--------------------------------------------------------------------------------
+data.test.test_my_policy: FAIL (0ms)
+
+  test.rego:8:
+    	x == y + z
+    	|    |   |
+    	|    |   3
+    	|    y + z: 5
+    	|    y: 2
+    	1
+
+SUMMARY
+--------------------------------------------------------------------------------
+test.rego:
+data.test.test_foo: FAIL (0ms)
+--------------------------------------------------------------------------------
+FAIL: 1/1
+```
+
+Authored by @johanfylling, reported by @grosser.
+
+### Reading stdin in `opa exec` ([#6538](https://github.com/open-policy-agent/opa/issues/6538))
+
+The `opa exec` command now supports reading `input` documents from stdin with the `--stdin-input` (`-I`) flag.
+E.g.:
+
+```shell
+$ echo '{"user": "alice"}' | opa exec --stdin-input --bundle my_bundle
+```
+
+Authored by @colinjlacy, reported by @humbertoc-silva.
+
+### Topdown and Rego
+
+- ast: Fix blanket "unexpected assign token" error message / usability issue ([#6563](https://github.com/open-policy-agent/opa/issues/6563)) authored by @anderseknert
+- ast: Fix wrong location on metadata parse errors on first line ([#6587](https://github.com/open-policy-agent/opa/issues/6587)) authored by @anderseknert
+- ast: Fix/inspect unknowns in with stmt ([#6812](https://github.com/open-policy-agent/opa/issues/6812)) authored by @johanfylling reported by @surajupadhyay01
+- ast: Include original text in annotation location text attribute ([#6779](https://github.com/open-policy-agent/opa/issues/6779)) authored by @anderseknert
+- ast: Expanding nested expressions in `every` domain ([#6790](https://github.com/open-policy-agent/opa/issues/6790)) authored by @johanfylling reported by @anakrish
+- topdown: Add http.send request attribute to ignore headers for caching key ([#6642](https://github.com/open-policy-agent/opa/issues/6642)) authored and reported by @rudrakhp
+
+### Runtime, Tooling, SDK
+
+- build: Use chainguard images from dockerhub ([#6830](https://github.com/open-policy-agent/opa/pull/6830)) authored by @srenatus
+- bundle: Preallocate buffers for file contents. ([#6818](https://github.com/open-policy-agent/opa/pull/6818)) authored by @philipaconrad
+- plugins: Reduce locks during decision logging ([#6797](https://github.com/open-policy-agent/opa/pull/6797)) authored by @mjungsbluth
+- plugins/rest: Do local map modification in OAuth2 client credentials flow ([#6769](https://github.com/open-policy-agent/opa/issues/6769)) authored and reported by @eubaranov
+- loader: Use a better error message when trying to merge non-objects ([#6803](https://github.com/open-policy-agent/opa/issues/6803)) authored by @anderseknert
+- server/authorizer: Fix gzip payload handling ([#6804](https://github.com/open-policy-agent/opa/issues/6804)) authored by @philipaconrad reported by @nevumx
+
+### Docs, Website, Ecosystem
+
+- docs: Remove missing prometheus metric `go_memstats_gc_cpu_fraction` ([#6783](https://github.com/open-policy-agent/opa/issues/6783)) authored by @philipaconrad
+- docs: Mention that default functions may not evaluate ([#6265](https://github.com/open-policy-agent/opa/issues/6265)) authored by @anderseknert
+- docs: Fix spelling and grammar of `an HTTP` ([#6786](https://github.com/open-policy-agent/opa/pull/6786)) authored by @jdbaldry
+- docs/website: Add vs code and zed to ecosystem page ([#6788](https://github.com/open-policy-agent/opa/pull/6788)) authored by @charlieegan3
+- docs/website: Add Flipt to the OPA ecosystem ([#6781](https://github.com/open-policy-agent/opa/pull/6781)) authored by @markphelps
+- docs/website: Add Flipt blog to their ecosystem page ([#6789](https://github.com/open-policy-agent/opa/pull/6789)) authored by @charlieegan3
+- docs/website: Revise language SDK content ([#6811](https://github.com/open-policy-agent/opa/pull/6811)) authored by @charlieegan3
+
+### Miscellaneous
+
+- Dependency updates; notably:
+  - build(go): bump golang from 1.22.3 to 1.22.4
+  - build(deps): bump github.com/containerd/containerd from 1.7.17 to 1.7.18
+  - build(deps): bump golang.org/x/net from 0.25.0 to 0.26.0
 
 ## 0.65.0