Add a transpose command to concrete index notation

[willow-ahrens]

TACO currently treats transposition as a user-space operation, but an important first step to making things more automatic is to add a construct to transpose on compute(). https://github.com/tensor-compiler/taco/issues/496 addresses allocation of the transposed tensor, but it should also be pointed out here that we need to allocate the result of the transpose automatically. This would allow for transpose and reformat operations to occur automatically as prescribed by an autoscheduler in concrete index notation.