Add basic modflowapi example (#17) #87

Job	Run time
Lint	16s
Install gw3099 environment on linux (3.9)	4m 18s
Install gw3099 environment (macos-latest, 3.9)	4m 53s
Install gw3099 environment on linux (3.10)	4m 49s
Install viz environment (ubuntu-latest, 3.9)	1m 55s
Install gw3099 environment (macos-latest, 3.10)	4m 15s
Install gw3099 environment on linux (3.11)	4m 8s
Install gw3099 environment (macos-latest, 3.11)	4m 50s
Install viz environment (ubuntu-latest, 3.10)	2m 3s
Install gw3099 environment (windows-latest, 3.9)	11m 27s
Install viz environment (ubuntu-latest, 3.11)	1m 55s
Install gw3099 environment (windows-latest, 3.10)	12m 47s
Install viz environment (macos-latest, 3.9)	3m 8s
Install gw3099 environment (windows-latest, 3.11)	9m 20s
Install viz environment (macos-latest, 3.10)	3m 33s
Install viz environment (macos-latest, 3.11)	2m 1s
Install viz environment (windows-latest, 3.9)	8m 26s
Install viz environment (windows-latest, 3.10)	7m 1s
Install viz environment (windows-latest, 3.11)	10m 8s
	1h 41m 13s

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