feat(common): QuotaUserOption for gRPC-based libs

[coryan]

Fixes #13928

---

This change is 

[dbolduc]

Putting this in the metadata decorator would be more consistent:

google-cloud-cpp/google/cloud/storage/internal/storage_metadata_decorator.cc

Lines 879 to 887 in 4db2434

	if (options.has<UserProjectOption>()) {
	context.AddMetadata("x-goog-user-project",
	options.get<UserProjectOption>());
	}
	auto const& authority = options.get<AuthorityOption>();
	if (!authority.empty()) context.set_authority(authority);
	for (auto const& h : options.get<CustomHeadersOption>()) {
	context.AddMetadata(h.first, h.second);
	}

[coryan]

Hmm... if anything, the metadata decorator should not set these common options and just call a common function to do it.

[dbolduc]

if anything, the metadata decorator should not set these common options and just call a common function to do it.

Sure, that will save us N lines of code per service.

---

I sort of think that the base stub should call ConfigureContext(), instead of the retry loops calling it.

Part of the reason why I would steer you away from ConfigureContext() is that I don't trust its coverage. For example, the polling loops do not use it:

google-cloud-cpp/google/cloud/internal/async_polling_loop.cc

Line 81 in 4db2434

ConfigurePollContext(*context, *options_);

[coryan]

Let's merge #13935 and then I can make the changes to that function, would that work?

[dbolduc]

SGTM

[coryan]

PTAL.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.12%. Comparing base (18f522e) to head (a694a5b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13933   +/-   ##
=======================================
  Coverage   93.12%   93.12%           
=======================================
  Files        2181     2181           
  Lines      185840   185870   +30     
=======================================
+ Hits       173065   173098   +33     
+ Misses      12775    12772    -3     

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[devbww]

s/QuotaUser/QuotaUserOption/?

[coryan]

Fixed.

[devbww]

Was "system parameter" supposed to be a link?

[coryan]

Yes, fixed in #13937