Updates to VoyageEmbedding (#11721)

* - refactor the base
 - adding new test case to validate the code works with API key stored as env.variable

* Batch size default value

* Remove unused constant
Correct the code

* Corrections due to comments

* Corrections
New tests

* Adding truncation attribute
Refactoring
Remove useless test

* Remove default model
Add tests
Reformat, etc

---------

Co-authored-by: fodizoltan <zoltan@conway.expert>