Required. The name of the topic. It must have the format
"projects/{project}/topics/{topic}". {topic} must
start with a letter, and contain only letters ([A-Za-z]),
numbers ([0-9]), dashes (-), underscores (_),
periods (.), tildes (````), plus (+) or percent signs
(%). It must be between 3 and 255 characters in length,
and it must not start with"goog"``.
Policy constraining the set of Google Cloud Platform regions
where messages published to the topic may be stored. If not
present, then no constraints are in effect.
