TopicName.parse could throw a more detailed ValidationException

[SimonScholz]

Recently I faced an issue when using the Topic.parse(String formattedString) method, because the String being used was an environment variable defined within a pod.
I could've been faster in resolving the issue, if the formattedString originating from the environment variable would be printed out as part of the ValidationException's message.

Also see my PR for this minor improvement: #1505

Current behavior:

The message TopicName.parse: formattedString not in valid format is shown.

throw new ValidationException("TopicName.parse: formattedString not in valid format");

Expected / desired behavior:

The message TopicName.parse: formattedString (${actual value of formattedString}) not in valid format is shown.

throw new ValidationException(
        "TopicName.parse: formattedString (%s) not in valid format", formattedString);

[maitrimangal]

Hi, your last PR was inside of an autogenerated class which is why I could not approve it-

java-pubsub/proto-google-cloud-pubsub-v1/src/main/java/com/google/pubsub/v1/TopicName.java

Line 31 in 8ded110

// AUTO-GENERATED DOCUMENTATION AND CLASS.

Will find out how to write into that file!