Re-add the option for asset_eol_date as an import field

[uberbrady]

[fd-36545] We had this before, but due to a refactor it somehow got merged out :/

I tested this by uploading a CSV with a specific EOL date set in a column, and mapping that (well, it auto-mapped), and then importing, and then making sure that the assets showed up with that EOL date. That worked.

[what-the-diff]

PR Summary

• Introduction of 'asset_eol_date' to mount() function
  The addition of a new field named 'asset_eol_date' to the mount() function in Importer.php. This will improve how the system manages and tracks the end-of-life dates for various assets, enhancing the overall asset management within the system.

[snipe]

I don't really understand how that got refactored out. That change was just added in May.

[snipe]

Thanks for re-adding it tho!