feat: extract output with regexes from LLMs (#3491)

* feat: extract output with regexes from LLMs

This changset adds `extract_regex` to the LLM config. It is a list of
regexes that can match output and will be used to re extract text from
the LLM output. This is particularly useful for LLMs which outputs final
results into tags.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* Add tests, enhance output in case of configuration error

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

core/backend/backend_suite_test.go

@@ -0,0 +1,13 @@
+package backend_test
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestBackend(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Backend test suite")
+}