Requests a short-lived OAuth access token from the Axway gateway using
client credentials. Requires APOLLO_CLIENT_ID, APOLLO_CLIENT_SECRET,
and APOLLO_TOKEN_URL to be set in .Renviron.
Use usethis::edit_r_environ() to set them. Only relevant for BI.
Examples
if (FALSE) { # \dontrun{
token <- get_apollo_token()
} # }