[Tuner] Automatic merging of tuner-generated td specs

[kuhar]

We should be able to automatically append the best spec selected by the tuner to an existing tuning spec file.

This can be done either through textual manipulation of a spec file with some markers that indicate where new tuning specs should go, or as an iree pass similar to the one that links tuning specs. The main difference compared to the latter one is that we would like to keep adding new specs to an existing transform.foreach_match in %arg0 op in the main named sequence called __kernel_config.