main : option to disable context shift (#9484)

* added cli arg to disable context shift

* reverted precommit

* updated README.md for main

* white space

* allow disabling context shift in the server

* Update common/arg.cpp

no-context-shift only works for main example

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

* added server example to --no-context-shift args

* removed server changes

* white space

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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>