feat(legacyCreateProxyMiddleware): show migration tips

[chimurai]

Description

Display upgrade tips when legacyCreateProxyMiddleware() is used with legacy features.

Motivation and Context

DX;
Allow users to use legacyCreateProxyMiddleware() as intermediate upgrade, before fully migrating to v3

How has this been tested?

• unit tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[coveralls]

Coverage increased (+0.05%) to 97.872% when pulling a4e7d64 on legacy-migration-tips into cdfe934 on v3.