CmdStan User's Guide - method `optimize` - document argument for jacobian adjustment

#### Summary:

Documentation to accompany implementation of https://github.com/stan-dev/cmdstan/issues/1124.

#### Description:

PR https://github.com/stan-dev/stan/pull/3152 allows us to run optimization with/without the jacobian adjustment.
Document this.

#### Additional Information:
Provide any additional information here.

#### Current Version:
v2.30.0
