ENH Improve GridFieldExportButton csv export filename

[3Dgoo]

Description

This change improves the GridFieldExportButton csv export filename.

Currently the export filename is always the following no matter what the model is:

export-$now.csv

With a date format of:

d-m-Y-H-i

The developer cannot modify this. If the cms user is exporting multiple models, they all have the same name, making it hard to differentiate between exports. The time stamp of d-m-Y-H-i is not necessarily ideal.

This PR changes the default csv export file name to:

[classname]-export-[timestamp].csv

With a default date format of:

Y-m-d-H-i-s

The [classname] will automatically be replaced with the model classname. Resulting in the following example filenames:

order-export-2024-11-07-23-15-20.csv
product-export-2024-11-07-23-16-59.csv

The filename and date format can also be easily changed on a per button basis through the code.

Manual testing steps

Go to the CMS security section:

/admin/security/

Press Export CSV.

Observer file name.

Issues

#11458

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[3Dgoo]

To do: Make those two variables yml configurable