[limes] use global.is_global_region in helm-charts

[wagnerd3]

• use global.is_global_region instead of deriving this info from the limes_url
• use customer_domains = ["global"] from the values for the global region (less special logic)
• replace contains "iaas-" with hasPrefix "iaas-" for more robustness

[sapcc-bot]

Failed to validate the helm chart. Details. Readme.

[majewsky]

I presume you already ran this against global-qa? If not, please check the diff on CI.

[wagnerd3]

I did not, else I would have seen that like for billing chart in global, we are missing the global:globals values. I will revert for now and check with you tomorrow whether the diff is fine, I found something odd there.