Unable to increase the memory of gen2 functions beyond 512mb

[tgerulaitis]

Steps to replicate:

1. Configure a GCP function with version set to gen2 and memory set to a value greater than 512.
2. Build and deploy the function to GCP.

Expected outcome:

The function is deployed successfully and is allocated the correct amount of memory.

Actual outcome:

Deployment fails with the following error:

Invalid value specified for container memory. For 0.333 CPU, memory must be between 128Mi and 512Mi inclusive.

Notes:

It would be nice to automatically select the appropriate minimal value of CPU for the amount of memory the user has specified, but also add a cpu runtime config parameter to allow overriding that value. This way the solution would remain backwards compatible.