incompatible_auto_exec_groups

Flag: --incompatible_auto_exec_groups
Available since: Bazel 7
Flipped in: not yet
Planner removal: not yet

**Current status**
Implemented and almost ready to flip in Bazel@Head.

**Short summary**
Automatic execution groups select an execution platform for each toolchain type. In other words, one target can have multiple execution platforms without defining execution groups. Migration requires setting a toolchain parameter inside ctx.actions.{run, run_shell} for actions which use tool or executable from a toolchain.

**More information**
* [Migration guideline](https://bazel.build/extending/auto-exec-groups#migration-aegs)
* [Official Bazel Documentation about AEGs](https://bazel.build/extending/auto-exec-groups)
* [Bazel Github Issue - Migration of Automatic Exec Groups](https://github.com/bazelbuild/bazel/issues/19981)
* [Design Document - Exec platform per toolchain](https://docs.google.com/document/d/1-rbP_hmKs9D639YWw5F_JyxPxL2bi6dSmmvj_WXak9M/edit?usp=sharing)