feat: [functions] add available_cpu field (#4092)

* feat: add `available_cpu ` field
feat: add `kms_key_name` field to ServiceConfig (the CMEK use case)
feat: add `max_instance_request_concurrency` field
feat: add `security_level` field

PiperOrigin-RevId: 516979219

Source-Link: googleapis/googleapis@650f7cd

Source-Link: googleapis/googleapis-gen@3c4d23f
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