add EcoAssistant blog

[JieyuZ2]

Why are these changes needed?

Add a blog introducing EcoAssistant

Related issue number

N/A

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[JieyuZ2]

@microsoft-github-policy-service agree

[codecov-commenter]

Codecov Report

Merging #647 (4f23622) into main (337ac4c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #647   +/-   ##
=======================================
  Coverage   28.72%   28.72%           
=======================================
  Files          27       27           
  Lines        3380     3380           
  Branches      760      760           
=======================================
  Hits          971      971           
  Misses       2338     2338           
  Partials       71       71           

Flag	Coverage Δ
unittests	28.66% <ø> (ø)

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[sonichi]

Both code formatting check and doc checks fail.

[sonichi]

you can use pre-commit to help with the formatting.

[JieyuZ2]

you can use pre-commit to help with the formatting.

yes. all checks are passed now