fix(pubsub): add commit schema and list schema revision samples

[alevenberg]

Issue #11720

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This change is 

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• google/cloud/pubsub/samples/samples.cc:840, tag pubsub_commit_avro_schema
• google/cloud/pubsub/samples/samples.cc:869, tag pubsub_commit_proto_schema
• google/cloud/pubsub/samples/samples.cc:933, tag pubsub_list_schema_revisions

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[codecov]

Codecov Report

Patch coverage: 61.81% and project coverage change: +0.01 🎉

Comparison is base (0754b6e) 93.78% compared to head (b1f4885) 93.79%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11840      +/-   ##
==========================================
+ Coverage   93.78%   93.79%   +0.01%     
==========================================
  Files        1838     1838              
  Lines      166295   166350      +55     
==========================================
+ Hits       155956   156032      +76     
+ Misses      10339    10318      -21     

Impacted Files	Coverage Δ
google/cloud/pubsub/samples/samples.cc	87.20% <61.81%> (-1.05%)	⬇️

... and 4 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
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[dbolduc]

nit: This type of PR should be a doc(pubsub) instead of a fix(pubsub).

(Oops, I am too late on the review. It's not a big deal. Just use doc for the next one).

[dbolduc]

FYI: The second tag is unnecessary and can be removed. (unless you plan to write a doc that links it). Here's why...

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There are two types of tags for samples.

The first tag [START pubsub_commit_avro_schema] is used by the DevRel teams. These tags denote samples that show up on https://cloud.google.com/pubsub/docs/samples (for example).

The second tag, [commit-avro-schema], is something our team uses to include samples in our documentation.

For example, the google::cloud::pubsub::Publisher:

google-cloud-cpp/google/cloud/pubsub/publisher.h

Line 75 in facd5b4

* @snippet samples.cc custom-thread-pool-publisher

.... links to this sample:

google-cloud-cpp/google/cloud/pubsub/samples/samples.cc

Lines 1400 to 1439 in facd5b4

	//! [custom-thread-pool-publisher]
	namespace pubsub = ::google::cloud::pubsub;
	using ::google::cloud::future;
	using ::google::cloud::GrpcCompletionQueueOption;
	using ::google::cloud::Options;
	using ::google::cloud::StatusOr;
	[](std::string project_id, std::string topic_id) {
	// Create our own completion queue to run the background activity, such as
	// flushing the publisher.
	google::cloud::CompletionQueue cq;
	// Setup one or more of threads to service this completion queue. These must
	// remain running until all the work is done.
	std::vector<std::thread> tasks;
	std::generate_n(std::back_inserter(tasks), 4, [&cq] {
	return std::thread([cq]() mutable { cq.Run(); });
	});
	auto topic = pubsub::Topic(std::move(project_id), std::move(topic_id));
	auto publisher = pubsub::Publisher(pubsub::MakePublisherConnection(
	std::move(topic), Options{}.set<GrpcCompletionQueueOption>(cq)));
	std::vector<future<void>> ids;
	for (char const* data : {"1", "2", "3", "go!"}) {
	ids.push_back(
	publisher.Publish(pubsub::MessageBuilder().SetData(data).Build())
	.then([data](future<StatusOr<std::string>> f) {
	auto s = f.get();
	if (!s) return;
	std::cout << "Sent '" << data << "' (" << *s << ")\n";
	}));
	}
	publisher.Flush();
	// Block until they are actually sent.
	for (auto& id : ids) id.get();
	// Shutdown the completion queue and join the threads
	cq.Shutdown();
	for (auto& t : tasks) t.join();
	}
	//! [custom-thread-pool-publisher]

... which results in the following documentation:

https://cloud.google.com/cpp/docs/reference/pubsub/latest/classgoogle_1_1cloud_1_1pubsub_1_1Publisher#example-using-a-custom-thread-pool

[alevenberg]

Ah i see will send a PR to fix

[0000854453]