Break up Basic pallet example into smaller pallets

[sacha-l]

The Basic Example pallet is really useful but could probably be broken down into smaller example pallets, focusing on the different things it demonstrates for e.g.:

• different ways to configure weights
• examples of signed extensions
• examples of storages
• best practices for using internal public/private functions

Although this pallet has basic functionality in terms of what it does it by no means is basic 🫠

[kianenigma]

I think a lot of these topics are essentially reference docs and should be moved to this format, as opposed to an example pallet. See my comment in https://github.com/paritytech/polkadot-sdk/pull/1554#pullrequestreview-1629925100. Suggest concluding this before making example pallets.