Unsuppressable start up message

[achafetz]

When running a package check on any of our packages, one check that provides a warning is about whether the startup messages can be suppressed. This arises for all our packages since they all have gagglr::oha_check().

While class = "packageStartupMessage" was added as a param for all of the cli messages in check_updates(), following what is done in tidyverse it appears we should create a function that outputs the message using rlang::inform(msg, ..., class = "packageStartupMessage")

https://github.com/tidyverse/tidyverse/blob/62f32d43e1e0650e4c05632dbfbe06977d1f292f/R/zzz.R#L2C1-L5C4

https://github.com/tidyverse/tidyverse/blob/62f32d43e1e0650e4c05632dbfbe06977d1f292f/R/utils.R#L1-L10