Add script example for node operation.

Thanks @skyriter for picking this up.
The only examples we have right now are Test and so they are prefixed as such.

This one should be prefixed with Example ... something like /src/cbo_scripts/ExampleProcessNodeContent.php

My thinking is that inside /src/cbo_scripts we will either have Tests or Examples. The main difference being that Tests can be expected to run harmlessly, and Examples should never be run.

Sorry @skywriter I just noticed you had code in the fork. I didn't see a Merge Request so I didn't know anything was there.

I just pushed up a PR with an example from something we are doing on CMS.

I just merged mine. But I don't want to discard yours @skyriter. Yours still exists here
https://git.drupalcode.org/issue/codit_batch_operations-3425031/-/commit...
but would need an MR.
A couple things I see that might need work

1. The extension needs to be .php.txt so it does not get picked up as actual code and throw an error in the UI.
2. There are some large commented out sections that are confusing to me. I am guessing they are still a work in progress.