Support of custom functions for the scatter op in TTNN dialect.

[ajakovljevicTT]

During lowering of the stablehlo.scatter op, there was an issue with lowering the full functionality of the op, since the StableHLO version also accepts a function which denotes an operation used in combining both the target at scattered tensor. Currently, this is not used in any model that we have tried on. However, there is a jax operation scatter_add where this function is a simple add, suggesting the need for it (see: https://jax.readthedocs.io/en/latest/_autosummary/jax.lax.scatter_add.html). It is possible to decompose this and leave the intricacies of this function out of tt-metal, since it does not currently support this, nor indexing in scatter (issue in metal: tenstorrent/tt-metal#4294).