Soft delete

Rules for AIP-164, covering soft delete.

Rule name	Description
`http-body`	Undelete methods should use `*` as the HTTP body.
`http-method`	Undelete methods must use the POST HTTP verb.
`http-uri-suffix`	Undelete methods must have the correct URI suffix
`request-message-name`	Undelete methods must have standardized request message names.
`request-name-behavior`	Undelete RPCs should annotate the `name` field with `google.api.field_behavior`.
`request-name-field`	Undelete RPCs must have a `name` field in the request.
`request-name-reference`	Undelete RPCs should annotate the `name` field with `google.api.resource_reference`.
`request-unknown-fields`	Undelete RPCs should not have unexpected fields in the request.
`resource-expire-time-field`	Resources supporting soft delete must have an `expire_time` field.
`response-lro`	Declarative-friendly undelete methods should use long-running operations.
`response-message-name`	Undelete methods must return the resource.

Note: Because AIPs sometimes cover topics that have some overlap, some rules related to soft delete may be included in the rules for other AIPs.