Rename the "executorch/examples/sdk" folder to "executorch/examples/devtools" (#5207)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/5207

This is part of the bigger renaming "sdk" -> "devtools" task.
Renaming principles:
1. Replace "sdk" in the file paths to "devtools", that is, "fbcode/executorch/examples/**sdk**" -> "fbcode/executorch/examples/**devtools**";
2. When parent path has the word "devtools" in it, then the child paths do not include "devtools" anymore *to reduce redundancy*, e.g., "fbcode/executorch/examples/**sdk/sdk_example_runner**" -> "fbcode/executorch/examples/**devtools/example_runner**"

Reviewed By: dbort

Differential Revision: D62409715

fbshipit-source-id: 00ee0dc540349d85ba344d07e0000dcc5205b74d