Fix cluster name parsing logic

[jpraychev]

What this PR does / why we need it:
The PR fixes the metric.attributes.cluster dimensions to provide the whole hostname, as with the current parsing logic, only a subset (mainly only the api string) of the hostname is presented to the end user (on the respective backend). The information is not particularly useful if you want to determine which cluster the metric originates from, hence the current PR proposal:

For example, the following cluster https://api.c-123456.stage.kyma.ondemand.com, results in just api on the backend. The same goes for MCP cluster naming convention as well.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

Fixes hostname parsing logic