feat: r/demo/foo20airdrop - Merkle Airdrop contract example #1046

Job	Run time
test (1.20.x, _test.flappy)	50s
test (1.20.x, _test.pkg.amino)	5m 19s
build (1.20.x, amd64, linux, ./pkg/amino/cmd/aminoscan)	30s
test (1.20.x, _test.pkg.bft)	5m 7s
build (1.20.x, amd64, linux, ./pkg/amino/cmd/goscan)	23s
test (1.20.x, _test.pkg.others)	5m 27s
build (1.20.x, amd64, linux, ./pkg/autofile/cmd)	38s
test (1.21.x, _test.flappy)	46s
build (1.20.x, amd64, linux, ./pkg/iavl/cmd/iaviewer)	23s
test (1.21.x, _test.pkg.amino)	4m 40s
build (1.21.x, amd64, linux, ./pkg/amino/cmd/aminoscan)	18s
test (1.21.x, _test.pkg.bft)	4m 24s
build (1.21.x, amd64, linux, ./pkg/amino/cmd/goscan)	21s
test (1.21.x, _test.pkg.others)	5m 24s
build (1.21.x, amd64, linux, ./pkg/autofile/cmd)	19s
build (1.21.x, amd64, linux, ./pkg/iavl/cmd/iaviewer)	30s
upload-coverage	10s
	35m 29s

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