feat: specify an ovn underlay network through MicroOVN #1405

Job	Run time
Code	1m 52s
System (1.22.x, add)	22m 31s
System (1.22.x, instances)	21m 14s
documentation-checks / Run documentation checks	1m 5s
System (1.22.x, basic)	21m 30s
System (1.22.x, recover)	19m 18s
System (1.22.x, interactive)	18m 2s
System (1.22.x, mismatch)	21m 3s
System (1.22.x, preseed)	21m 9s
Trigger snap edge build	1s
	2h 27m 45s

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