Dialogflow EntityType Resource

[c2thorn]

Fixes hashicorp/terraform-provider-google#5513

Release Note Template for Downstream PRs (will be copied)

`google_dialogflow_entity_type`

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 5 files changed, 698 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 5 files changed, 698 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 117 insertions(+))

[megan07]

Looks good!