First aggregate function support

[lakshmanan-v]

It would be nice to have FIRST() aggregate function that returns the first value in a bucket (similar to LASTWITHTIME function).

cc @Jackie-Jiang @weixiangsun

[anilprabhala]

@lakshmanan-v @weixiangsun Would love to contribute here. Can I pick this up?

[lakshmanan-v]

Awesome. Thanks. Go for it @anilprabhala. If you have time, please consider functions like the majority value (pick the value which occurs most in the aggregation) along with first().

[anilprabhala]

Will do. Thanks @lakshmanan-v

[weixiangsun]

Thanks @anilprabhala for taking the first function.