[Fix] Correctly generate classes with nested body fields (#808)

## Changes
Correctly generate classes with nested body fields. 

### Backwards incompatible changes
The next time code is generated, the following backward incompatible
changes will happen:
* Removal of the following classes: `apps.CreateAppDeploymentRequest`,
`apps.CreateAppRequest`, `apps.UpdateAppRequest`,
`catalog.CreateOnlineTableRequest`, `dashboards.CreateDashboardRequest`,
`dashboards.CreateScheduleRequest`,
`dashboards.CreateSubscriptionRequest`,
`dashboards.UpdateDashboardRequest` and
`dashboards.UpdateScheduleRequest`
* Change of signature for the following methods: `AppsAPI.create`,
`AppsAPI.create_and_wait`, `AppsAPI.deploy`, `AppsAPI.deploy_and_wait`,
`AppsAPI.update`, `OnlineTablesAPI.create`,
`OnlineTablesAPI.create_and_wait`, `LakeviewAPI.create`,
`LakeviewAPI.create_schedule`, `LakeviewAPI.create_subscription`,
`LakeviewAPI.update` and `LakeviewAPI.update_schedule`. Each of those
methods now take an object instead of a list of parameters.

## Tests
Preview

66ce450

- [ ] `make test` run locally
- [ ] `make fmt` applied
- [ ] relevant integration tests applied

Author: hectorcast-db

.codegen/service.py.tmpl

@@ -240,6 +240,9 @@ class {{.PascalName}}API:{{if .Description}}
 {{- end}}
 
 {{define "method-serialize" -}}
+        {{if and .Request.HasJsonField .RequestBodyField -}}
+        body = {{template "safe-snake-name" .RequestBodyField}}
+        {{- else -}}
         {{if or .Request.HasJsonField .Request.HasQueryField -}}
         {{if .Request.HasJsonField}}body = {}{{end}}{{if .Request.HasQueryField}}
         query = {}{{end}}
@@ -251,6 +254,7 @@ class {{.PascalName}}API:{{if .Description}}
         {{- end}}
         {{- end}}
         {{- end}}
+        {{- end}}
 {{- end}}
 
 {{ define "method-headers" -}}