[Feature] create_aggregate() missing

[Daholli]

create_aggregate() currently missing

as far as I can tell create_aggregate currently does not exist, I was changing lots of my code and suddenly ran into this error, I will just not use the function for now but I would love to see this added

• OS: Windows
• Python version: 3.11.2
• aiosqlite version: 0.19
• Can you repro on 'main' branch? yes
• Can you repro in a clean virtualenv? yes

[Daholli]

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