[GCP] Improve metadata collectors caching

[gpop63]

NewMetadataService is executed based on the period set in the config e.g. 1m, so the in memory maps we're using for caching aren't actually helping, we're still fetching fresh data every time.

We need proper caching for all metadata collectors:

• compute
• cloudsql
• redis
• dataproc (once it's merged)

It could be made configurable to be refreshed every hour/12h/day etc.