Use .clj_kondo extension for hook code (#487)

This helps avoid issues with tooling that assumes
.clj files on the classpath are loadable.

See clj-kondo/clj-kondo#1685
and https://github.com/clj-kondo/clj-kondo/blob/master/doc/hooks.md#refreshing-with-toolsnamespace

CHANGELOG.md

@@ -3,6 +3,7 @@ This is a history of changes to clara-rules.
 # 0.23.0-SNAPSHOT
 * extract clara.rules.compiler/compile-test-handler from clara.rules.compiler/compile-test
 * add support for `env` inside of test expressions
+* use `.clj_kondo` extension for clj-kondo hook code for better tool compatibility (clj-kondo support now requires clj-kondo 2022.04.25 or higher)
 
 # 0.22.1
 * fix incorrent lint warning triggered when this binding is not used in clj-kondo hooks

CONTRIBUTORS.md

@@ -12,6 +12,7 @@ Community
 - Dave Dixon [@sparkofreason]
 - Baptiste Fontaine [@bfontaine]
 - Jose Gomez [@k13gomez]
+- Imre Kószó [@imrekoszo]
 
 [@rbrush]: https://github.com/rbrush
 [@mrrodriguez]: https://github.com/mrrodriguez
@@ -23,3 +24,4 @@ Community
 [@bfontaine]: https://github.com/bfontaine
 [@sunilgunisetty]: https://github.com/sunilgunisetty
 [@k13gomez]: https://github.com/k13gomez
+[@imrekoszo]: https://github.com/imrekoszo