Move all example pallets under `examples` folder. (#10215)

* Put all examples under one folder

Signed-off-by: Jimmy Chu <jimmychu0807@gmail.com>

* Updated Cargo.toml

Signed-off-by: Jimmy Chu <jimmychu0807@gmail.com>

* updated for ci script

Signed-off-by: Jimmy Chu <jimmychu0807@gmail.com>

* update

Signed-off-by: Jimmy Chu <jimmychu0807@gmail.com>

* Added notes that example pallets are not meant to be used in production.

Signed-off-by: Jimmy Chu <jimmychu0807@gmail.com>

* updated

Signed-off-by: Jimmy Chu <jimmychu0807@gmail.com>