Implement client$runtimes to get all runtimes

[gshotwell]

We currently have client$server_settings_r but I couldn't find a good way to get everything. Here's a possible implementation:

library(connectapi)
library(purrr)
client <- connect()

tidy_settings <- function(type = c("r", "python", "quarto")) {
  type = match.arg(type)
  settings = client$GET(paste0("v1/server_settings/", type))
  out = map_dfr(settings$installations, ~as.data.frame(.))
  out$runtime = type
  return(out[, c("runtime", "version")])
}

map_dfr(c("python", "r", "quarto"), tidy_settings)

[toph-allen]

Added as get_runtimes(client) in #320.