[Feature/Improvement]: Deprecate Legacy Methods (client.legacy) and update documentation

### Summary

Update documentation to feature the new `datacube`

### Problem statement

Documentation doesn't highlight latest features

### Proposed solution (optional)

_No response_

### Alternatives considered (optional)

_No response_

### Additional context (optional)

_No response_

No files or tests are named. Start by locating the documentation and references to client.legacy and datacube, then confirm which legacy methods are deprecated and how datacube should be presented. Done means the documentation highlights datacube and accurately explains the legacy-method transition.

Written by the indexing model from the issue text.