Configure memoization storage at spec level

# Summary

Currently memoization storage is configured at step level. Configuring at workflow level would be more user friendly.

# Motivation

To reduce time and effort configuring memoization.

# Proposal

`/spec/memoization/cache` or similar.

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**Message from the maintainers**:

If you wish to see this enhancement implemented please add a 👍 reaction to this issue! We often sort issues this way to know what to prioritize.

Start by reading how memoization storage is currently configured at the step level and how workflow specifications are structured. Define the proposed spec-level location, such as /spec/memoization/cache, and confirm that configuring it at workflow level reduces repeated step configuration.

Written by the indexing model from the issue text.