Agent: Update protobuf definition for agent configuration

MR: Add default and max workspace resources protobuf (gitlab-org/cluster-integration/gitlab-agent!1192 - merged)

Description

Add new json fields - default_resources_per_workspace_container and max_resources_per_workspace for the agent configuration. These are non-required fields.

The structure of both these fields is

        limits:
            cpu: "1"
            memory: 500m
        requests:
            cpu: 500m
            memory: 500Mi

Acceptance Criteria

• Two new non-required json fields are added to the agent configuration.
• The structure of each of them matches what is mentioned above.
• Within the field, all values are required.
• Value of memory would be a string
• Value of cpu would be a string