Replace `atlas_citation` with alternative citation method

[daxkellie]

At the moment, the only atlas_ function that doesn't return any data is atlas_citation, and as a result it is a little bit confusing. It could be easier to add the citation info as part of the data object, which can be extracted using a citation function from another package

[daxkellie]

I've changed my mind about this function. What it does well is place lots of useful information in one convenient place. I think it requires some formatting updates, but can remain as is for now.

There is a possibility to change the name to collect_citation() in a future version to be consistent with expected syntax changes in the next version of {galah}