Support AddToDefinition (add new field to feature service)

[JosiahParry]

Discussed in #177

^{Originally posted by sarahhurley March 27, 2024}
Hi there - I am wondering if there is the capability of adding a field to a feature layer through the arcgislayers package? I'm working on setting up a workflow that may require us to add a field to a dataset over time (trying to avoid needing to republish it every time). I've tried to look through the documentation, but I've only found in the "Overwrite Hosted Feature Layer" section of the R-ArcGIS Bridge documentation a line that says "Truncating a service does not change the field definitions or permit us to add or remove fields to it. If you wish to do so, publish a new layer instead."

Thanks for your help!

[JosiahParry]

For reference: #177 (comment)

@mmachir helped provide a sample POST request which should be easy to mimic in R

request url - 
https://services1.arcgis.com/unique-id-here/arcgis/rest/admin/services/heart_binary/FeatureServer/0/addToDefinition
 
method-
POST
 
payload - 
f: 
json
addToDefinition: 
{"fields":[{"name":"testfieldname","type":"esriFieldTypeString","alias":"Test Display Name","nullable":true,"editable":true,"length":256,"defaultValue":"~de fault-value!"}]}
token:  redacted

This should be fairly simple to mimic:

b_req <- arc_base_req(x[["url"]], path = "addToDefinition")
httr2::req_form_body(
    b_req,
    fields = fields_json
)

[JosiahParry]

Note that this would allow us to also add related tables https://community.esri.com/t5/arcgis-online-questions/adding-related-table-to-arcgis-online-feature/td-p/252845

this could be a useful workflow when there are tables that have many matches to single polygons. Repeating the polygons is not ideal.