Implement Content Vanity API

[tdstein]

Content Vanity API

v0.6.0 Proposal

from posit import connect

client = connect.Client()
content = client.content.get(...)

vanity = content.vanity = ...
del content.vanity

vanity.destroy()

[nealrichardson]

Following https://github.com/rstudio/connect/pull/27252, we should add vanity_url to the default include specification (and also add include to the content item GET request). Then for the vanity_url @property, if the field is not set, do GET /__api__/v1/content/{guid}/vanity to resolve it (that API was added in 2020: https://github.com/rstudio/connect/pull/18448).

Ideally we should be able to distinguish between "There is no vanity URL for this content" and "I haven't asked for the vanity URL yet" so we don't make extra requests, but that's probably not a huge concern (until we learn otherwise).