Update/create steps needed to configure m10n Add credit

[arlina-espinoza]

After changes done in #223 and apigee/apigee-devportal-kickstart-drupal#323, we need to update the documentation to match.

1. Kickstart docs: Update instructions for setting up monetization during installer
2. Kickstart docs: Update/create how to install monetization after installing if not done during installer
3. M10n docs: Update/create Steps needed to configure m10n

[cnovak]

@arshad can you lay out any details needed for @jbennett13 to update, or update docs yourself?

[shadcn]

1. Kickstart docs: Update instructions for setting up monetization during installer

Do we have docs for setting up monetization in Kickstart? I couldn't find it.

2. Kickstart docs: Update/create how to install monetization after installing if not done during installer

If you do not enable monetization during instllation, then the steps are similar to apigee_m10n. These docs still applies. See also the notes below.

3. M10n docs: Update/create Steps needed to configure m10n

So I looked at the docs for enabling monetization, the only thing that changed is that now that requirement.module is in apigee_m10n, we could add a note to the Add Credit documentation to let users know they can follow suggestions from the requirement reports to quickly setup add credit.

Something along the lines of: "Apigee Monetization module ships with suggestions (helpers?) to quickly setup Add credit. See the requirements report at Reports --> Requirements Report."

[jbennett13]

Updated here: https://www.drupal.org/docs/8/modules/apigee-monetization/enable-the-apigee-monetization-add-credit-module