NIFI-6586 - Code comments and doc updates

[YolandaMDavis]

Posting as a draft because for some reason the Admin Guide updates aren't showing as expected. @mattyb149 or @achristianson if you can help identify what I am missing?

Thank you for submitting a contribution to Apache NiFi.

Please provide a short description of the PR here:

Description of PR

Enables X functionality; fixes bug NIFI-YYYY.

In order to streamline the review of the contribution we ask you
to ensure the following steps have been taken:

For all changes:

• Is there a JIRA ticket associated with this PR? Is it referenced
  in the commit message?

• Does your PR title start with NIFI-XXXX where XXXX is the JIRA number you are trying to resolve? Pay particular attention to the hyphen "-" character.

• Has your PR been rebased against the latest commit within the target branch (typically master)?

• Is your initial contribution a single, squashed commit? Additional commits in response to PR reviewer feedback should be made on this branch and pushed to allow change tracking. Do not squash or use --force when pushing to allow for clean monitoring of changes.

For code changes:

• Have you ensured that the full suite of tests is executed via mvn -Pcontrib-check clean install at the root nifi folder?
• Have you written or updated unit tests to verify your changes?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE file, including the main LICENSE file under nifi-assembly?
• If applicable, have you updated the NOTICE file, including the main NOTICE file found under nifi-assembly?
• If adding new Properties, have you added .displayName in addition to .name (programmatic access) for each of the new properties?

For documentation related changes:

• Have you ensured that format looks appropriate for the output in which it is rendered?

Note:

Please ensure that once the PR is submitted, you check travis-ci for build issues and submit an update to your PR as soon as possible.

[ai-christianson]

We should note what the keys/values are/mean.

[ai-christianson]

I.e. what is the string, what is the long.

[YolandaMDavis]

@achristianson thanks for the feedback, I've made changes to clarify this

[ai-christianson]

We may want to go in some detail about caching policy, as well as the nature of the cache (in-memory, size, etc.).

[YolandaMDavis]

Makes sense, have added info

[ai-christianson]

Thanks for taking the time to put together good code documentation. Nothing stuck out which would be a blocker, but I left a couple notes on things that we could potentially expound.

[YolandaMDavis]

@achristianson I made a few more changes to include some detail on the framework in the user and admin guides. Also I figured out my issue with seeing docs updated locally so I moved this PR out of draft mode.

[ai-christianson]

@YolandaMDavis I rebased analytics-framework branch onto master and now it is reporting conflicts. Once those are resolved I can merge into the branch.

[YolandaMDavis]

@achristianson merged this request so closing PR manually

[ottobackwards]

What happens if they aren't available? Will it tell you? Can you tell the difference between not enough data and not configured?

[YolandaMDavis]

@ottobackwards thanks for this question, it prompted us to ensure we add enabled/disabled property for the new features (commit has been added to the PR against master #3681. UI changes are pending (did ask @rfellows offline) but in short tooltip will distinguish when predictions are enabled yet not available vs when predictions are not enabled.