Rename metrics without units

[vmercierfr]

Objective

Specify units for rds_replication_slot_disk_usage_average and rds_usage_allocated_storage_average

Why

According to Prometheus metrics best practices, these metrics should contain the _bytes suffix instead of _average

rds_usage_allocated_storage_average was specified in Gigabytes while it should be in Bytes.

How

• Rename rds_replication_slot_disk_usage_average to rds_replication_slot_disk_usage_bytes
• Rename rds_usage_allocated_storage_average to rds_usage_allocated_storage_bytes

Issue was reported by end-user in https://github.com/qonto/prometheus-rds-exporter/issues/32

Release plan

• [ ] Merge this PR
• [ ] Update metrics in Grafana dashboards
• [ ] Update alerts in Database Monitoring Framework

[vmercierfr]

sre

[github-actions[bot]]

Package	Line Rate	Health
github.com/qonto/prometheus-rds-exporter/internal/app/cloudwatch	88%	✔
github.com/qonto/prometheus-rds-exporter/internal/app/ec2	88%	✔
github.com/qonto/prometheus-rds-exporter/internal/app/rds	79%	➖
github.com/qonto/prometheus-rds-exporter/internal/app/servicequotas	51%	❌
github.com/qonto/prometheus-rds-exporter/internal/app/unit	100%	✔
Summary	82% (523 / 640)	✔

Minimum allowed line rate is 60%