Redis enterprise prometheus v2 metrics

[foogaro]

What does this PR do?

Updates the redis_enterprise_prometheus dashboards to use the new V2 metrics.

Motivation

The dashboards in the DataDog tenant already use V2 metrics, but the repository does not yet reflect this update.

[jeremyplichta]

Can you check these possible v1 metrics

./CHANGELOG.md:* Added node_cert_expiration_seconds to Node metrics
./README.md:passed on to Datadog. The individual metrics should be stripped of their prefix, e.g., 'rdse.bdb_up' would
./README.md:become 'bdb_up'. The full list of metrics is available on the 'Data Collected' tab of the integration page, or via the link in the [Metrics](#metrics) section.
./README.md:| RDSE.FLASH       | rdse.node_available_flash   | All flash metrics are of the form: rdse.node_*_flash |
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse.redis_process_cpu_system_seconds_total{$cluster,$db} by {bdb,redis}"
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse.redis_process_main_thread_cpu_user_seconds_total{$cluster,$db} by {bdb,redis}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                      "query": "avg:rdse.redis_process_cpu_usage_percent{$cluster, $node} by {redis}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                      "query": "avg:rdse.node_cpu_user{$cluster, $node}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                      "query": "avg:rdse.node_cpu_system{$cluster, $node}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                      "query": "sum:rdse.redis_keys_trimmed{$cluster, $node} by {redis}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                      "query": "sum:rdse.redis_evicted_keys{$cluster, $node} by {redis}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                      "query": "avg:rdse.node_total_req{*}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                "query": "avg:rdse.redis_blocked_clients{$cluster, $node} by {redis}"
./assets/dashboards/redis_enterprise-prometheus_node.json:                "query": "avg:rdse.redis_connected_clients{$cluster, $node} by {redis}"
./datadog_checks/redis_enterprise_prometheus/metrics.py:#     'node_available_flash': 'node_available_flash',
./datadog_checks/redis_enterprise_prometheus/metrics.py:#     'node_available_flash_no_overbooking': 'node_available_flash_no_overbooking',
./datadog_checks/redis_enterprise_prometheus/metrics.py:#     'node_provisional_flash': 'node_provisional_flash',
./datadog_checks/redis_enterprise_prometheus/metrics.py:#     'node_provisional_flash_no_overbooking': 'node_provisional_flash_no_overbooking',

also, bdb mentions

./README.md:passed on to Datadog. The individual metrics should be stripped of their prefix, e.g., 'rdse.bdb_up' would
./README.md:become 'bdb_up'. The full list of metrics is available on the 'Data Collected' tab of the integration page, or via the link in the [Metrics](#metrics) section.
./README.md:| RDSE.DATABASE    | rdse.bdb_                   | This will return replication metrics as well         |
./README.md:| RDSE.REPLICATION | rdse.bdb_crdt_              |                                                      |
./README.md:| RDSE.REPLICATION | rdse.bdb_replicaof_         |                                                      |
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse2.redis_server_mem_replication_backlog{$cluster,$db} by {bdb,redis}"
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse.redis_process_cpu_system_seconds_total{$cluster,$db} by {bdb,redis}"
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse.redis_process_main_thread_cpu_user_seconds_total{$cluster,$db} by {bdb,redis}"
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse2.redis_server_mem_fragmentation_ratio{$cluster,$db} by {bdb}"
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse2.redis_server_allocator_active{$cluster,$db} by {bdb,redis}"
./assets/dashboards/redis_enterprise-prometheus_shard.json:                      "query": "avg:rdse2.redis_server_allocator_allocated{$cluster,$db} by {bdb,redis}"

@slorello89 - any thoughts on this? Lets try to get this merged in this week to our fork then we can open PR to DD