Consolidate `get_usage_shiny()` and `get_usage_static()` into `get_views()`

[nealrichardson]

Following the model of https://github.com/posit-dev/posit-sdk-py/pull/170, conceal from the user the fact that there are different REST APIs for different content types and just present a single way to get usage stats for all types.

[jonkeane]

This is the same as #218 yeah?

[nealrichardson]

Yep looks like it

[kmasiello]

Consolidating some comments from a separate slack thread...

let's seek to return one usage data frame, regardless of content type, but keep a consistent and predictable column schema. If the content type does not have relevant data, keep the column in the output but return NA.

Suggesting "usage" over "views" because the latter isn't descriptive of programmatic access to APIs or pin reads.