obj_check_token error message should indicate how to create a token

[JosiahParry]

As title describes. Current error message is below. Users might not know how to create an authorization token. The message should indicate how to create a token if needed.

arcgisutils::obj_check_token(NULL)
#> Error:
#> ! `token` must be an <httr2_token> not <NULL>
#> Backtrace:
#>     ▆
#>  1. └─arcgisutils::obj_check_token(NULL)
#>  2.   └─cli::cli_abort(...) at arcgisutils/R/arc-token.R:128:5
#>  3.     └─rlang::abort(...)

^{Created on 2024-03-20 with reprex v2.0.2}