RCORE-2181 Add a testing websocket server

[jbreams]

What, How & Why?

☑️ ToDos

• 📝 Changelog update
• 🚦 Tests (or not relevant)
• C-API, if public C++ API changed
• bindgen/spec.yml, if public C++ API changed

[coveralls-official]

Pull Request Test Coverage Report for Build jonathan.reams_3392

Details

• 12 of 377 (3.18%) changed or added relevant lines in 4 files are covered.
• 38 unchanged lines in 10 files lost coverage.
• Overall coverage decreased (-0.1%) to 90.962%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/realm/sync/network/network_error.cpp	11	31	35.48%
test/websocket_server.hpp	0	20	0.0%
test/websocket_server.cpp	0	325	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/realm/query_engine.hpp	1	93.94%
test/fuzz_tester.hpp	1	57.73%
test/test_table.cpp	1	99.51%
src/realm/util/future.hpp	3	95.45%
test/fuzz_group.cpp	3	42.9%
src/realm/alloc_slab.cpp	4	90.56%
src/realm/link_translator.cpp	4	76.92%
src/realm/util/flat_map.hpp	4	96.12%
src/realm/bplustree.cpp	6	72.55%
src/realm/sync/noinst/server/server.cpp	11	73.87%

Totals
Change from base Build 2552:	-0.1%
Covered Lines:	217299
Relevant Lines:	238891

---

💛 - Coveralls

[evergreen-ci-prod]

There is an existing patch(es) for this commit SHA:

• Evergreen patch with PR

Please note that the status that is posted is not in the context of this PR but rather the (latest) existing patch and that may affect some tests that may depend on the particular PR. If your tests do not rely on any PR-specific values (like base or head branch name) then your tests will report the same status. If you would like a patch to run in the context of this PR and abort the other(s), comment 'evergreen retry'.