[FEATURE] Include RDS Proxy Metrics in the RDS namespace

[jfentontyro]

Is there an existing issue for this?

• [X] I have searched the existing issues

Feature description

RDS Proxy metrics show up in AWS under the AWS/RDS namespace in Cloudwatch Metrics. Currently they aren't retrieved when including the relevant RDS Proxy metric name in our config under the RDS namespace with the correct search tags.

This is due to the db-proxy resource filter not being supported, given it is supported in the resourcegroupstagging api supporting this filter under the RDS namespace should allow us to retrieve these metrics

What might the configuration look like?

{
    Namespace: "AWS/RDS",
    Alias:     "rds",
    ResourceFilters: []*string{
        aws.String("rds:db"),
        aws.String("rds:cluster"),
        aws.String("rds:db-proxy"),
    },
    DimensionRegexps: []*regexp.Regexp{
        regexp.MustCompile(":cluster:(?P<DBClusterIdentifier>[^/]+)"),
        regexp.MustCompile(":db:(?P<DBInstanceIdentifier>[^/]+)"),
        regexp.MustCompile(":db-proxy:(?P<ProxyIdentifier>[^/]+)"),
    },
},

Anything else?

No response

[jfentontyro]

I've tested this locally and works as expected, and this passes all existing service tests. DB proxy metrics appear in local prometheus container running against our AWS account and had no issues. I would raise a PR for this as it's a 2 line change in the services.go file but am unable to push.

Could you have a look at this when you get a chance please @cristiangreco