JSON field childs are not omitted

**Describe the bug**
Not sure if this should be considered as a bug, but if I use second level jsonPayload JSON childs with `modify_fields` and `omit_if`, first level JSON child (parent of second level child) then is not omitted.

**To Reproduce**
Steps to reproduce the behavior:
1. Start a GCE VM with image 'rocky-linux-9-v20240515'
2. Install Ops Agent version 'google-cloud-ops-agent-2.55.0-1.el9.x86_64.rpm'
3. Customize the agent with the following configuration' and restart the agent
```
logging:
receivers:
test_log:
type: tcp
format: json
processors:
add_context:
type: modify_fields
fields:
jsonPayload.serviceContext.service:
static_value: 'my-service'
omit_if: jsonPayload.exception = ""
service:
pipelines:
default_pipeline:
processors: [add_context]
receivers: [test_log]
```
This will leave empty `serviceContext: {}` in jsonPayload when exception field is empty.

The workaround I found is to use second processor to remove empty `serviceContext`:
```
logging:
receivers:
test_log:
type: tcp
format: json
processors:
omit_empty_context:
type: modify_fields
fields:
jsonPayload.serviceContext:
move_from: jsonPayload.serviceContext
omit_if: jsonPayload.exception = ""
add_context:
type: modify_fields
fields:
jsonPayload.serviceContext.service:
static_value: 'my-service'
omit_if: jsonPayload.exception = ""
service:
pipelines:
default_pipeline:
processors: [add_context, omit_empty_context]
receivers: [test_log]
```

This correctly doesn't produce `serviceContext` when exception is empty at all.

**Expected behavior**
It would be great if `modify_fields` could omit the field completely.

**Environment (please complete the following information):**
- VM distro / OS: Rocky Linux 9.5
- Ops Agent version 2.55.0