feat: add metrics for counting objects indiviual by gvr and in total

[akesser]

This pull request adds a metric for each gvr to count the number of observed objects of this gvr and a metric to count the total number of observed objects.

E.g. if you cluster metrics includes GroupPolicyAttachment.iam.crossplane.io, the metric to count the objects looks like this:

# TYPE iam_aws_crossplane_io_GroupPolicyAttachment_v1beta1_resource_count gauge
# HELP iam_aws_crossplane_io_GroupPolicyAttachment_v1beta1_resource_count A metrics series objects to count objects of iam_aws_crossplane_io_GroupPolicyAttachment_v1beta1
iam_aws_crossplane_io_GroupPolicyAttachment_v1beta1_resource_count 1

The metric to count all objects looks like the following:

# TYPE x_metric_resources_count_total gauge
# HELP x_metric_resources_count_total A metric to count all resources
x_metric_resources_count_total 6

[haarchri]

tested the implementation - thanks for this - LGTM

[haarchri]

@akesser please bump the versions in Chart.yaml and values.yaml