[feature request] add option to introduce io-uring for Commit

[fuweid]

Currently, when bbolt commits changes, the writeAt operations are sequential.
This proposal is trying to introduce io-uring to submit multiple writing operations in one time.
Since io-uring is kernel level feature, it's not always available. So, it will be optional and by default disable.
The detail design is still WIP and I will share it later via google doc.

cc @gangli113

[greenblade29]

Hi @fuweid , please let me know if I can be of any help. I would love to contribute once the detail design is done.