feat: refactor and improve K8s sync provider (#443)

## This PR
fixes #434

This is a refactoring and internal improvement for K8s ISync provider.

Improvements include,

- Reduce K8s API load by utilizing Informer cache
- Yet, provide a fallback if cache miss occurs (Note - we rely on K8s
Informer for cache refill and consistency)
- Informer now only watches a specific namespace (compared to **\***) -
this is a potential performance improvement and a security improvement
- Reduced informer handlers with extracted common logics 
- Unit tests where possible

---------

Signed-off-by: Kavindu Dodanduwa <kavindudodanduwa@gmail.com>

go.mod

@@ -37,7 +37,6 @@ require (
 	google.golang.org/grpc v1.53.0
 	google.golang.org/protobuf v1.28.1
 	gopkg.in/yaml.v3 v3.0.1
-	k8s.io/api v0.26.2
 	k8s.io/apimachinery v0.26.2
 	k8s.io/client-go v0.26.2
 	sigs.k8s.io/controller-runtime v0.14.5
@@ -115,6 +114,7 @@ require (
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
+	k8s.io/api v0.26.2 // indirect
 	k8s.io/apiextensions-apiserver v0.26.1 // indirect
 	k8s.io/component-base v0.26.1 // indirect
 	k8s.io/klog/v2 v2.90.0 // indirect

go.sum

@@ -285,18 +285,12 @@ github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8m
 github.com/onsi/ginkgo v1.16.5 h1:8xi0RTUf59SOSfEtZMvwTvXYMzG4gV23XVHOZiXNtnE=
 github.com/onsi/ginkgo/v2 v2.6.0 h1:9t9b9vRUbFq3C4qKFCGkVuq/fIHji802N1nrtkh1mNc=
 github.com/onsi/gomega v1.24.1 h1:KORJXNNTzJXzu4ScJWssJfJMnJ+2QJqhoQSRwNlze9E=
-github.com/open-feature/go-sdk v1.1.0 h1:JOOa0AleJFUvnWoF9KWdLqYosi5fDIRBDzPYZPr5qgM=
-github.com/open-feature/go-sdk v1.1.0/go.mod h1:R8QJmLdSHFaRdrWtwmp5bVK35Q+O/cEGtYaiy6NM6kc=
 github.com/open-feature/go-sdk v1.2.0 h1:2xsUgNUUDITpryB9nFS43CI9gAF415I1He22Q1d4+Po=
 github.com/open-feature/go-sdk v1.2.0/go.mod h1:UQJJXUptk92An4F6so2Vd0iRo6EEZ+QGa7HVyQ/GPi0=
-github.com/open-feature/go-sdk-contrib/providers/flagd v0.1.7 h1:0s8reX/EfCNV37PsGSr55wUpppPtyp0jZKeuVAaWZ+4=
-github.com/open-feature/go-sdk-contrib/providers/flagd v0.1.7/go.mod h1:dHB0hsYykZ1Un+CdnWErqLqUQswUADIvDg2VwDLx7gs=
 github.com/open-feature/go-sdk-contrib/providers/flagd v0.1.9 h1:hHa7sjOzohj9ZhYR6ym+Xjk517ogb4q2QIE6ztdLZMg=
 github.com/open-feature/go-sdk-contrib/providers/flagd v0.1.9/go.mod h1:IibpAPNmtUIJsJA6T4X1IcD4+BG1hCLw86luG8YQcqA=
 github.com/open-feature/go-sdk-contrib/tests/flagd v1.2.1 h1:Tg712Egcqb5dsYxOGEaQbfD3g1mqPFdV4tSmKKKxDPk=
 github.com/open-feature/go-sdk-contrib/tests/flagd v1.2.1/go.mod h1:zw/xpuDy9ziBEKVA1t4VoQtzFc80btAAQCiZkX6y9oQ=
-github.com/open-feature/open-feature-operator v0.2.28 h1:qzzVq8v9G7aXO7luocO/wQCGnTJjtcQh75mDOqjnFxo=
-github.com/open-feature/open-feature-operator v0.2.28/go.mod h1:bQncVK7hvhj5QStPwexxQ1aArPwox2Y1vWrVei/qIFg=
 github.com/open-feature/open-feature-operator v0.2.29 h1:Ky/SMzwEiBV5x9qOfHTj1jl/CakPZNClRtoeSPqVbNo=
 github.com/open-feature/open-feature-operator v0.2.29/go.mod h1:bQncVK7hvhj5QStPwexxQ1aArPwox2Y1vWrVei/qIFg=
 github.com/open-feature/schemas v0.2.8 h1:oA75hJXpOd9SFgmNI2IAxWZkwzQPUDm7Jyyh3q489wM=
@@ -359,7 +353,6 @@ github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
-github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
 github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
 github.com/stretchr/testify v1.8.2 h1:+h33VjcLVPDHtOdpUCuF+7gSuG3yGIftsP1YvFihtJ8=
 github.com/stretchr/testify v1.8.2/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
@@ -756,18 +749,12 @@ honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWh
 honnef.co/go/tools v0.0.1-2019.2.3/go.mod h1:a3bituU0lyd329TUQxRnasdCoJDkEUEAqEt0JzvZhAg=
 honnef.co/go/tools v0.0.1-2020.1.3/go.mod h1:X/FiERA/W4tHapMX5mGpAtMSVEeEUOyHaw9vFzvIQ3k=
 honnef.co/go/tools v0.0.1-2020.1.4/go.mod h1:X/FiERA/W4tHapMX5mGpAtMSVEeEUOyHaw9vFzvIQ3k=
-k8s.io/api v0.26.1 h1:f+SWYiPd/GsiWwVRz+NbFyCgvv75Pk9NK6dlkZgpCRQ=
-k8s.io/api v0.26.1/go.mod h1:xd/GBNgR0f707+ATNyPmQ1oyKSgndzXij81FzWGsejg=
 k8s.io/api v0.26.2 h1:dM3cinp3PGB6asOySalOZxEG4CZ0IAdJsrYZXE/ovGQ=
 k8s.io/api v0.26.2/go.mod h1:1kjMQsFE+QHPfskEcVNgL3+Hp88B80uj0QtSOlj8itU=
 k8s.io/apiextensions-apiserver v0.26.1 h1:cB8h1SRk6e/+i3NOrQgSFij1B2S0Y0wDoNl66bn8RMI=
 k8s.io/apiextensions-apiserver v0.26.1/go.mod h1:AptjOSXDGuE0JICx/Em15PaoO7buLwTs0dGleIHixSM=
-k8s.io/apimachinery v0.26.1 h1:8EZ/eGJL+hY/MYCNwhmDzVqq2lPl3N3Bo8rvweJwXUQ=
-k8s.io/apimachinery v0.26.1/go.mod h1:tnPmbONNJ7ByJNz9+n9kMjNP8ON+1qoAIIC70lztu74=
 k8s.io/apimachinery v0.26.2 h1:da1u3D5wfR5u2RpLhE/ZtZS2P7QvDgLZTi9wrNZl/tQ=
 k8s.io/apimachinery v0.26.2/go.mod h1:ats7nN1LExKHvJ9TmwootT00Yz05MuYqPXEXaVeOy5I=
-k8s.io/client-go v0.26.1 h1:87CXzYJnAMGaa/IDDfRdhTzxk/wzGZ+/HUQpqgVSZXU=
-k8s.io/client-go v0.26.1/go.mod h1:IWNSglg+rQ3OcvDkhY6+QLeasV4OYHDjdqeWkDQZwGE=
 k8s.io/client-go v0.26.2 h1:s1WkVujHX3kTp4Zn4yGNFK+dlDXy1bAAkIl+cFAiuYI=
 k8s.io/client-go v0.26.2/go.mod h1:u5EjOuSyBa09yqqyY7m3abZeovO/7D/WehVVlZ2qcqU=
 k8s.io/component-base v0.26.1 h1:4ahudpeQXHZL5kko+iDHqLj/FSGAEUnSVO0EBbgDd+4=