add cmake target and config export for parmmg to support find package #285

Job	Run time
parmmg-debug / ci (ubuntu-20.04, on, on, on, off)	54m 53s
parmmg-debug / ci (ubuntu-20.04, on, on, off, off)	42m 44s
parmmg-debug / ci (ubuntu-20.04, on, off, on, off)	54m 59s
parmmg-debug / ci (ubuntu-20.04, on, off, off, off)	42m 16s
parmmg-debug / ci (ubuntu-20.04, off, on, on, off)	54m 36s
parmmg-debug / ci (ubuntu-20.04, off, on, off, off)	42m 4s
parmmg-debug / ci (ubuntu-20.04, off, off, on, off)	56m 49s
parmmg-debug / ci (ubuntu-20.04, off, off, off, off)	47m 0s
parmmg-debug / ci (macos-12, on, on, on, off)	48m 48s
parmmg-debug / ci (macos-12, on, on, off, off)	18m 20s
parmmg-debug / ci (macos-12, on, off, on, off)	48m 30s
parmmg-debug / ci (macos-12, on, off, off, off)	19m 28s
parmmg-debug / ci (macos-12, off, on, on, off)	48m 1s
parmmg-debug / ci (macos-12, off, on, off, off)	19m 28s
parmmg-debug / ci (macos-12, off, off, on, off)	47m 51s
parmmg-debug / ci (macos-12, off, off, off, off)	18m 13s
parmmg-debug / ci (ubuntu-20.04, off, off, off, on)	1h 10m 6s
parmmg-debug / ci (ubuntu-20.04, off, off, on, on)	1h 11m 8s
parmmg-debug / ci (macos-12, off, off, off, on)	25m 59s
parmmg-debug / upload_coverage	47s
	13h 52m 0s

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