[redisstorageextension] allow redis key prefix to be specified in config

[HubertFraczek]

Description

The purpose of this PR is to allow the user to specify the redis key prefix. The lack of this feature has become problematic when using multiple replicas in a kubernetes cluster - until now, the key prefix has been based on the storage extension and receiver names, which are the same for each replica because they share the same configuration and therefore overwrite the same key in redis. With the changes in this PR, the user can specify the prefix as an environmental variable (which can have different value for each replica), for example.

Testing

opentelemetry-collector-contrib (0.118.0) was built with this change and tested on a kubernetes cluster

Config used for testing:

redis_storage:
  endpoint: redis.monitoring.svc.cluster.local:6379
  prefix: ${K8S_NODE_NAME}

Documentation

Updated README.md to add new config parameter.

[linux-foundation-easycla]

• ✅login: HubertFraczek / (a270e3f)

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