PMM-13597 Move `pmm-doc` v3 to monorepo #13821

Job	Run time
Tests (mysql:5.6, mongo:4.4, postgres:13, perconalab/pmm-server:3-dev-latest)	3m 57s
Tests (mysql:5.7, mongo:5.0, postgres:14, perconalab/pmm-server:3-dev-latest)	4m 21s
Tests (mysql:8.0, mongo:6.0, postgres:15, perconalab/pmm-server:3-dev-latest)	4m 17s
Tests (mysql:lts, mongo:7.0, postgres:16, perconalab/pmm-server:3-dev-latest)	3m 55s
Tests (mysql:latest, mongo:latest, postgres:latest, perconalab/pmm-server:3-dev-latest)	3m 56s
Tests (percona:5.6, percona/percona-server-mongodb:4.4, perconalab/percona-distribution-postgresq...	3m 56s
Tests (percona:5.7, percona/percona-server-mongodb:5.0, perconalab/percona-distribution-postgresq...	4m 1s
Tests (percona:8.0, percona/percona-server-mongodb:6.0, perconalab/percona-distribution-postgresq...	4m 19s
Tests (percona:8, percona/percona-server-mongodb:7.0, perconalab/percona-distribution-postgresql:...	4m 6s
Tests (percona:latest, percona/percona-server-mongodb:latest, perconalab/percona-distribution-pos...	4m 14s
Tests (mariadb:11.2, mongo:4.4, postgres:12, perconalab/pmm-server:3-dev-latest)	3m 54s
Tests (mariadb:11.4, percona/percona-server-mongodb:4.4, perconalab/percona-distribution-postgres...	3m 56s
Tests (mariadb:11.5, postgres:13, perconalab/pmm-server:3-dev-latest)	4m 6s
	52m 58s

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