bugfix: skip setting empty tags in request body

[ms-henglu]

fixes #462

In the following function, to suppress the diff of config: tags = null and state: tags = {}, it'll set plan.tags to {} even if it's not defined in config when upgrading from previous provider.

And this will fail the schema validation if the resource doesn't support "tags". And bypassing the validation won't mitigate this, because the empty tags will be set in the request body and user will get a bad request error.

The fix is adding tags to the request body only if it's not empty.

terraform-provider-azapi/internal/services/azapi_resource.go

Lines 858 to 880 in 192e61b

	func (r *AzapiResource) tagsWithDefaultTags(config types.Map, body map[string]interface{}, state *AzapiResourceModel, resourceDef *aztypes.ResourceType) types.Map {
	if config.IsNull() {
	switch {
	case body["tags"] != nil:
	return tags.FlattenTags(body["tags"])
	case len(r.ProviderData.Features.DefaultTags) != 0 && canResourceHaveProperty(resourceDef, "tags"):
	defaultTags := r.ProviderData.Features.DefaultTags
	if state == nil || state.Tags.IsNull() {
	return tags.FlattenTags(defaultTags)
	} else {
	currentTags := tags.ExpandTags(state.Tags)
	if !reflect.DeepEqual(currentTags, defaultTags) {
	return tags.FlattenTags(defaultTags)
	} else {
	return state.Tags
	}
	}
	// To suppress the diff of config: tags = null and state: tags = {}
	case state != nil && !state.Tags.IsUnknown() && len(state.Tags.Elements()) == 0:
	return state.Tags
	}
	}
	return config