Add peer provider plugin registration

[mantas-sidlauskas]

What changed?
Adding peer provider plugin registration code.

Why?
This code is going to be used to load external peer provider plugin. Peer provider plugin will provide an easy way to replace ringpop with another technology.

How did you test it?

Potential risks
None, this code is noop right now.

Related #5593

[coveralls]

Pull Request Test Coverage Report for Build 01907299-3fb0-4ecc-b0ad-df71b17f5ddc

Details

• 20 of 22 (90.91%) changed or added relevant lines in 1 file are covered.
• 36 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.005%) to 71.517%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
common/peerprovider/plugin.go	20	22	90.91%

Files with Coverage Reduction	New Missed Lines	%
common/mapq/types/policy_collection.go	2	93.06%
common/task/weighted_round_robin_task_scheduler.go	2	89.05%
service/matching/tasklist/db.go	2	73.23%
common/persistence/sql/sqlplugin/mysql/task.go	2	73.68%
service/matching/tasklist/matcher.go	2	90.91%
common/persistence/sql/sqlplugin/mysql/db.go	2	79.49%
common/persistence/historyManager.go	2	66.67%
common/log/tag/tags.go	3	49.64%
service/history/task/timer_standby_task_executor.go	3	85.63%
common/persistence/statsComputer.go	3	98.18%

Totals
Change from base Build 0190705f-c927-4d1b-b54d-772b615f64e2:	-0.005%
Covered Lines:	105326
Relevant Lines:	147274

---

💛 - Coveralls