[refactor] Move blackhole implementation to internal package (#6647)

## Which problem is this PR solving?
- Towards #6637

## Description of the changes
- This PR moves the implementation for blackhole storage from
`plugin/storage/` to `internal/storage/`

## How was this change tested?
- CI

## Checklist
- [x] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [x] I have signed all commits
- [x] I have added unit tests for the new functionality
- [x] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `npm run lint` and `npm run test`

---------

Signed-off-by: Mahad Zaryab <[email protected]>
Signed-off-by: Mahad Zaryab <[email protected]>

Author: mahadzaryab1

plugin/storage/blackhole/blackhole.go renamed to internal/storage/v1/blackhole/blackhole.go

@@ -15,13 +15,13 @@ import (
 
 	"github.com/jaegertracing/jaeger/internal/safeexpvar"
 	"github.com/jaegertracing/jaeger/internal/storage/v1/badger"
+	"github.com/jaegertracing/jaeger/internal/storage/v1/blackhole"
 	"github.com/jaegertracing/jaeger/internal/storage/v1/cassandra"
 	"github.com/jaegertracing/jaeger/internal/storage/v1/es"
 	"github.com/jaegertracing/jaeger/internal/storage/v1/grpc"
 	"github.com/jaegertracing/jaeger/internal/storage/v1/memory"
 	"github.com/jaegertracing/jaeger/pkg/metrics"
 	"github.com/jaegertracing/jaeger/plugin"
-	"github.com/jaegertracing/jaeger/plugin/storage/blackhole"
 	"github.com/jaegertracing/jaeger/plugin/storage/kafka"
 	"github.com/jaegertracing/jaeger/storage"
 	"github.com/jaegertracing/jaeger/storage/dependencystore"