Define label and help text for work's partOf search term

Problem Description: Work's partOf search term does not define a label or help text. As is, this prevents it from appearing in the advanced search form. Production users are presently prevented from using this search term. Per the advanced search configuration generator, this is the only term this is true for.

Expected Behavior/Solution: Define a label and help text such as the following (in userFacingConfig.mjs) but for work.partOf.

    aboutItem: {
      label: 'About Objects',
      helpText: 'Search for Works that are about the specified Objects.',
    },

Requirements: See above.

Needed for promotion: If an item on the list is not needed, it should be crossed off but not removed.

~- [ ] Wireframe/Mockup - Mike~

[ ] Committee discussions - Sarah
[ ] Feasibility/Team discussion - Sarah
[x] Backend requirements - Stated above.
[x] Frontend requirements - No frontend or middle tier changes are required.
[ ] Are new regression tests required for QA - Amy
[ ] Questions
List of questions for discussions. Answers should be documented within the issue.

UAT/LUX Examples: Make sure the search term becomes available in the advanced search form, on the Works search tab.

Dependencies/Blocks: This ticket neither blocks nor is blocking another ticket.

Related Github Issues: None

Related links: None

Wireframe/Mockup: N/A

project-lux / lux-marklogic

Define label and help text for work's partOf search term #291