Add a substitution Category Of Operations into ODT generation for Invoices

[warnerbryce]

I saw recently this PR : #23242
I tested it and it worked great for crabe and sponge PDF models.
For my personnal Dolibarr i use for Invoices an ODT Template.

This is my first PR in Dolibarr and i am not really a Dev, so i don't know if the things i wrote are OKAY or totally Awkward.
I tested this modification on my own test instance and it worked.

Hope this PR can be review or improved.

I just add a substitution string {object_category_operation}