[SEDONA-245] R include man pages + use pkgdown for package documentation

[gregleleu]

Did you read the Contributor Guide?

• Yes, I have read Contributor Rules and Contributor Development Guide

Is this PR related to a JIRA ticket?

• Yes, the URL of the associated JIRA ticket is https://issues.apache.org/jira/projects/SEDONA/issues/SEDONA-245. The PR name follows the format [SEDONA-XXX] my subject.

What changes were proposed in this PR?

• Update to the R documentation: fix typos, group functions of the same family together
• Add the man pages to GitHub repo: best practice in the R world, lets users install from GitHub with the help pages
• Use pkgdown to create a nice package website with articles
• Update the docs workflow to build the pkgdown site, removed the "generate-docs.R" file which is not needed anymore

Currently, the pkgdown site is a drop-in replacement of the previous R docs. They are buried under API > RDD > R. I believe they should be more visible.
Also, the current workflow does not run examples in the article because it does not have access to the jars. Long-term solution would be to chain workflows so that downstream workflows have access to build jars.

How was this patch tested?

Ran R CMD Check

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation update.