fix: unnest wasm samples from client, exclude it from workspace

[nxsaken]

Description

• move smartcontracts out of client/tests/integration
• rename smartcontracts to wasm_samples
• pin executor_custom_data_model version in client
• exclude wasm_samples from the workspace
• move default_executor to wasm_samples

Benefits

• fixes the error with cargo install:

  package `.../client/tests/integration/smartcontracts/executor_custom_data_model/Cargo.toml` 
  is a member of the wrong workspace

• wasm samples (executors, smartcontracts and triggers) are more discoverable

• Dependabot updates target all wasm samples instead of just the default executor

Checklist

• I've read CONTRIBUTING.md
• I've used the standard signed-off commit format (or will squash just before merging)
• All applicable CI checks pass (or I promised to make them pass later)
• (optional) I've written unit tests for the code changes
• I replied to all comments after code review, marking all implemented changes with thumbs up

[mversic]

I think the change is ok

[DCNick3]

I don't think that our default executor is a terribly useful example, but having all crates that compile into on-chain wasm in one place does sound logical.

We might also want to make it more apparent which of the wasm examples are smart contracts, triggers or executors. Some naming conventions are trying to appear (executors are prefixed with _executor, triggers have _trigger somewhere in the name, smart contracts do not have those), but multisig and multisig_register kind of break this convention currently.

[nxsaken]

@DCNick3 I attempted it in the previous iteration of this PR: #4850. There I also unnested iroha_executor and iroha_trigger from iroha_smart_contract. I might revisit it after this.

[github-actions]

@BAStos525