PMM-8655 Send unsent messages after connection problems #9300

Job	Run time
Tests (mysql:5.6, mongo:4.2, postgres:10, percona/pmm-server:2.0.0)	8m 2s
Tests (mysql:5.7, mongo:4.4, postgres:11, percona/pmm-server:2.0.1)	9m 3s
Tests (mysql:8.0, mongo:4.4, postgres:12, percona/pmm-server:2.1.0)	8m 8s
Tests (mysql:8.0, mongo:4.4, postgres:13, percona/pmm-server:2.2.0)	9m 34s
Tests (percona:5.6, percona/percona-server-mongodb:4.2, perconalab/percona-distribution-postgresq...	8m 51s
Tests (percona:5.7, percona/percona-server-mongodb:4.4, perconalab/percona-distribution-postgresq...	8m 22s
Tests (percona:8.0, percona/percona-server-mongodb:4.4, perconalab/percona-distribution-postgresq...	8m 40s
Tests (mariadb:10.2, mongo:4.4, postgres:9.4, perconalab/pmm-server:dev-latest)	8m 11s
Tests (mariadb:10.3, percona/percona-server-mongodb:4.4, postgres:9.5, perconalab/pmm-server:dev-...	9m 37s
Tests (mariadb:10.4, postgres:9.6, perconalab/pmm-server:dev-latest)	10m 30s
	1h 28m 58s

Provide feedback