docs: Add proposal for direct data transfer

[sesame0224]

What this PR does / why we need it

This PR proposes a new method for enabling direct data communication between Numaflow vertices, and describes the motivation and resource specifications.

Related issues

#2990
This PR is an initial design derived from the above post.
We would like to discuss this with the community.

Testing

This PR includes only documentation, so no tests were performed.

Special notes for reviewers

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.75%. Comparing base (7f28dc7) to head (a54f4d4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3125      +/-   ##
==========================================
+ Coverage   79.73%   79.75%   +0.02%     
==========================================
  Files         291      291              
  Lines       65143    65143              
==========================================
+ Hits        51941    51956      +15     
+ Misses      12649    12636      -13     
+ Partials      553      551       -2     

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