Add updated Cohere Embedding blueprint

[tianjing-li]

Description

[Describe what this change achieves]

Updates Cohere blueprint documentation, merging the two existing blueprints into one, as both were made to integrate the same /embed API call but with different model params. Clarifies some of the steps, and adds steps to optionally add ingestion pipeline.

Issues Resolved

N/A

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[tianjing-li]

There is also some documentation here: https://opensearch.org/docs/latest/ml-commons-plugin/remote-models/connectors/, I'd like to update it because some of the info is out of date - can someone point me to where that lives?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (bd8b6ab) 82.82% compared to head (a9c500a) 82.85%.
Report is 23 commits behind head on main.

❗ Current head a9c500a differs from pull request most recent head 23e7804. Consider uploading reports for the commit 23e7804 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1950      +/-   ##
============================================
+ Coverage     82.82%   82.85%   +0.02%     
- Complexity     5446     5450       +4     
============================================
  Files           522      522              
  Lines         21903    21903              
  Branches       2227     2227              
============================================
+ Hits          18142    18147       +5     
+ Misses         2852     2846       -6     
- Partials        909      910       +1     

Flag	Coverage Δ
ml-commons	82.85% <ø> (+0.02%)	⬆️

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[ylwu-amzn]

Line 108 to 127 is not needed, as user can see the model id directly from line 104

[tianjing-li]

@ylwu-amzn done