[experimental] Add functions for adding priority fees to transactions

[steveluscher]

I haven't thought what this will look like, but the principle is to offer a helper that you can use to transform a transaction into one that has a custom priority fee of your choosing.

Whoever takes this issue on, please flesh out this issue description with your ideas of what this API should look like.

[lorisleiva]

This should probably be an alias or wrapper of the generated function getSetComputeUnitPrice of the Compute Budget client. Meaning you'd need to import @solana/compute-budget-program in order to access that helper.