Form Complete Metadata Column for Supertibble

[rsh52]

Description

This is a very light PR adding in form_complete_pct as a metadata column to the supertibble. It summarizes the average of "Complete"s/2's for a given form (it does not take into account unverifieds, etc. which I don't think we can capture in one column).

Proposed Changes

List changes below in bullet format:

• Add form_complete_pct to supertibble metadata columns
• Update write_redcap_xlsx to appropriately handle percentage output (similar to data_na_pct)
• Update README image to show new column.

Issue Addressed

Closes #183

PR Checklist

Before submitting this PR, please check and verify below that the submission meets the below criteria:

• [x] New/revised functions have associated tests
• [NA] New/revised functions that update downstream outputs have associated static testing files (.RDS) updated under inst/testdata/create_test_data.R
• [NA] New/revised functions use appropriate naming conventions
• [x] New/revised functions don't repeat code
• [x] Code changes are less than 250 lines total
• [x] Issues linked to the PR using GitHub's list of keywords
• [x] The appropriate reviewer is assigned to the PR
• [x] The appropriate developers are assigned to the PR
• [x] Pre-release package version incremented using usethis::use_version()

Code Review

This section to be used by the reviewer and developers during Code Review after PR submission

Code Review Checklist

• [ ] I checked that new files follow naming conventions and are in the right place
• [ ] I checked that documentation is complete, clear, and without typos
• [ ] I added/edited comments to explain "why" not "how"
• [ ] I checked that all new variable and function names follow naming conventions
• [ ] I checked that new tests have been written for key business logic and/or bugs that this PR fixes
• [ ] I checked that new tests address important edge cases