compute_kernel_matrix: Computes kernel matrix
In scAlign: An alignment and integration method for single cell genomics

Adds the defined kernel to the operation graph for high dimensional pairwise data similarity

1 2	compute_kernel_matrix(data, data_shape, labels = NULL, method = NULL, perplexity = 30, diag = "zero")

`data`	cell x feature data matrix
`data_shape`	number of features for data
`labels`	cell x 1 annotation (label) vector
`method`	Kernel to compute pairwise cell similarity
`perplexity`	neighborhood parameter for gaussian kernel
`diag`	indicator for self similarity