fix(sdk): Dont require mimetype in manifest schema #6682

Job	Run time
Protocol Buffer Lint and Gencode Up-to-date check	26s
go (examples)	55s
image build	1m 54s
go (sdk)	1m 51s
integration tests	4m 25s
go (service)	3m 10s
go (lib/ocrypto)	47s
license check	58s
otdfctl e2e tests	4m 56s
go (lib/fixtures)	41s
go (lib/flattening)	54s
platform-xtest / cross-client-test	8m 48s
ci	1s
	29m 46s

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