submodule: bump openthread from f14d726 to 102a631 (#574)

Bumps [openthread](https://github.com/openthread/openthread) from `f14d726` to `102a631`.
- [Commits](openthread/openthread@f14d726...102a631)

---
updated-dependencies:
- dependency-name: openthread
  dependency-type: direct:production
...

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