use v1 content image API (2024.09.0)

[aronatkins]

The Connect 2024.09.0 release publicizes content image endpoints.

• GET /content/{guid}/__thumbnail__
• PUT /__api__/v1/content/:guid/thumbnail
• DELETE /__api__/v1/content/:guid/thumbnail

The connectapi functions to get, set, and delete content images need to prefer these public API paths.

https://github.com/rstudio/connectapi/blob/bfefb00ce4721c0bb80aedf58ae217ff63742bee/R/deploy.R#L423-L426
https://github.com/rstudio/connectapi/blob/bfefb00ce4721c0bb80aedf58ae217ff63742bee/R/deploy.R#L479

https://github.com/rstudio/connectapi/blob/bfefb00ce4721c0bb80aedf58ae217ff63742bee/R/deploy.R#L509-L512

https://github.com/rstudio/connectapi/blob/bfefb00ce4721c0bb80aedf58ae217ff63742bee/R/deploy.R#L465

### Tasks