[C++] Update ExecPlan example code and documentation with new options

[asfimport]

Reporter: Vibhatha Lakmal Abeykoon / @vibhatha
Assignee: Vibhatha Lakmal Abeykoon / @vibhatha

PRs and other links:

• GitHub Pull Request #12689

_{Note: This issue was originally created as ARROW-15515. Please see the migration documentation for further details.}

[asfimport]

Weston Pace / @westonpace:
Issue resolved by pull request 12689
#12689