etcd: add basic support

[bigbes]

• implemented etcd driver (backend) for basic storage
• used etcd testing.LazyCluster for integration testing
• modified .golangci.yaml to add new library exclusion

Part of #TNTP-4189

[coveralls]

Pull Request Test Coverage Report for Build 19138272403

Details

• 163 of 1201 (13.57%) changed or added relevant lines in 7 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-3.2%) to 18.858%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
driver/etcd/operation.go	20	26	76.92%
driver/etcd/predicate.go	37	51	72.55%
driver/etcd/etcd.go	101	129	78.29%
internal/testing/t.go	0	42	0.0%
internal/mocks/etcd_client_mock.go	0	222	0.0%
internal/mocks/etcd_txn_mock.go	0	726	0.0%

Files with Coverage Reduction	New Missed Lines	%
driver/etcd/etcd.go	1	77.86%
internal/testing/t.go	2	0.0%

Totals
Change from base Build 19101577872:	-3.2%
Covered Lines:	548
Relevant Lines:	2906

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💛 - Coveralls