enhance slime test: plugin and limiter

[believening]

The testing of the slime project has been enhanced in the following three points:

1. add integration test for plugin module (kubebuilder envtest)
2. add integration test for limiter module (kubebuilder envtest)
3. add test target in Makefile

And current test result:

$ make test
?       slime.io/slime/modules/limiter  [no test files]
?       slime.io/slime/modules/limiter/api/config       [no test files]
?       slime.io/slime/modules/limiter/api/v1alpha2     [no test files]
?       slime.io/slime/modules/limiter/controllers/multicluster [no test files]
?       slime.io/slime/modules/limiter/model    [no test files]
?       slime.io/slime/modules/limiter/module   [no test files]
?       slime.io/slime/modules/meshregistry     [no test files]
?       slime.io/slime/modules/meshregistry/api/v1alpha1        [no test files]
?       slime.io/slime/modules/meshregistry/controllers [no test files]
?       slime.io/slime/modules/meshregistry/model       [no test files]
?       slime.io/slime/modules/meshregistry/module      [no test files]
?       slime.io/slime/modules/meshregistry/pkg/features        [no test files]
?       slime.io/slime/modules/meshregistry/pkg/mcpoverxds      [no test files]
?       slime.io/slime/modules/meshregistry/pkg/monitoring      [no test files]
?       slime.io/slime/modules/meshregistry/pkg/multicluster    [no test files]
?       slime.io/slime/modules/meshregistry/pkg/server  [no test files]
ok      slime.io/slime/modules/limiter/controllers      26.827s coverage: 46.0% of statements
ok      slime.io/slime/modules/limiter/test/e2e 0.468s  coverage: [no statements]
ok      slime.io/slime/modules/meshregistry/pkg/bootstrap       0.278s  coverage: 35.6% of statements
ok      slime.io/slime/modules/meshregistry/pkg/source  0.349s  coverage: 47.6% of statements
?       slime.io/slime/modules/meshregistry/pkg/source/k8s      [no test files]
?       slime.io/slime/modules/meshregistry/pkg/source/k8s/fs   [no test files]
ok      slime.io/slime/modules/meshregistry/pkg/source/eureka   0.490s  coverage: 45.0% of statements
?       slime.io/slime/modules/meshregistry/pkg/util/cache      [no test files]
ok      slime.io/slime/modules/meshregistry/pkg/source/nacos    0.655s  coverage: 26.5% of statements
ok      slime.io/slime/modules/meshregistry/pkg/source/sourcetest       0.354s  coverage: 13.3% of statements
ok      slime.io/slime/modules/meshregistry/pkg/source/zookeeper        0.765s  coverage: 37.3% of statements
ok      slime.io/slime/modules/meshregistry/pkg/util    0.354s  coverage: 5.4% of statements
?       slime.io/slime/modules/plugin   [no test files]
?       slime.io/slime/modules/plugin/api/config        [no test files]
?       slime.io/slime/modules/plugin/api/v1alpha1      [no test files]
?       slime.io/slime/modules/plugin/model     [no test files]
?       slime.io/slime/modules/plugin/module    [no test files]
ok      slime.io/slime/modules/plugin/controllers       16.296s coverage: 37.2% of statements

[believening]

part of #487