Do not make assumptions about files in HMRC PAYE task

[barrucadu]

The documented list of files does not match the reality.

This also makes it much easier to load all the current files into the asset manager:

for file in *; do
    sudo -udeploy govuk_setenv asset-manager bundle exec rake govuk_assets:create_hmrc_paye_asset[$file]
done

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Trello card

[thomasleese]

Could we also add a Rake task that basically does the same as for * in file and you can upload a whole directory in one go?

Might also be worth adding some logging to let the user know it's working correctly.

[barrucadu]

I've only made it do all zip files, as the xml file needs its file name changing when uploaded.

[barrucadu]

create_or_replace_whitehall_asset already prints out on-disk filenames and legacy URL paths as it uploads things, so I don't think there's a need for extra logging