No build clause in root level `skaffold.yaml` inserts local.Builder, messing up GCB Concurrency

### Expected behavior
When I run `skaffold dev` on resources that all use Google Cloud Build and have default concurrency of parallel (0), they run in parallel.

### Actual behavior

Our builds run serially.

### Fix

Add the following clause to the base `skaffold.yaml`

```yaml
build:
googleCloudBuild: {}
```

### Information

skaffold version: v1.39.3
OS: Mac

yaml setup:

base `skaffold.yaml` that looks like this:

```yaml
# Master Skaffold
apiVersion: skaffold/v2beta12
kind: Config
metadata:
name: backends
requires:
- path: ./common
configs: [common]

- path: ./microservices/service1
configs: [service1]

- path: ./microservices/service2
configs: [service2]
```

Service yaml (we are targeting a build that uses custom profile and GCB).

```yaml
apiVersion: skaffold/v2beta12
kind: Config
metadata:
name: service1
requires:
- path: ../../common
configs: [common]
build:
tagPolicy:
gitCommit: {}
local:
concurrency: 0
artifacts:
- image: service1
requires:
- image: common
alias: BASE_IMG
sync:
infer:
- '**/*.py'
- '**/*.json'
portForward:
- resourceType: service
resourceName: service1
port: 80
localPort: 9031
deploy:
kustomize:
paths:
- ./kustomize/minikube
profiles:
- name: custom
build:
googleCloudBuild:
concurrency: 0
artifacts:
- image: service1
requires:
- image: common
alias: BASE_IMG
deploy:
kustomize:
paths:
- ./kustomize/custom
```

When we don't target a group of services with `-m service1,service2` and instead run just `skaffold dev`, a local builder gets inferred for the base `skaffold.yaml` even there there isn't a build clause, bringing concurrency to 1:

From logs:

```
time="2023-03-04T10:30:07-05:00" level=debug msg="parsed 1 configs from configuration file /Users/dhodun/developer/cloud-learning-platform/skaffold.yaml" subtask=-1 task=DevLoop
time="2023-03-04T10:30:07-05:00" level=debug msg="Defaulting build type to local build" subtask=-1 task=DevLoop
```
```
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency first set to 0 parsed from *gcb.Builder[0]" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency value 0 parsed from *gcb.Builder[1] is ignored since it's not less than previously set value 0" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency value 0 parsed from *gcb.Builder[2] is ignored since it's not less than previously set value 0" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency value 0 parsed from *gcb.Builder[3] is ignored since it's not less than previously set value 0" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency value 0 parsed from *gcb.Builder[4] is ignored since it's not less than previously set value 0" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency value 0 parsed from *gcb.Builder[5] is ignored since it's not less than previously set value 0" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency value 0 parsed from *gcb.Builder[6] is ignored since it's not less than previously set value 0" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="build concurrency updated to 1 parsed from *local.Builder[7]" subtask=-1 task=DevLoop
time="2023-03-04T10:30:10-05:00" level=info msg="final build concurrency value is 1" subtask=-1 task=DevLoop
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```