Hangfire MS SQL Server schema should use datetime2 instead of datetime

Hangfire MS SQL Server schema should use `datetime2` instead of `datetime`. This is really a minor issue in a sense. `datetime` data type is mostly deprecated, `datetime2 `does the job better. `datetime2 `offers also increase precision if that is required. But for just in-place replacement `datetime2(3)` can be used.

`datetime `does some rounding also so currently the timestamps aren't really accurate to 100 fractional seconds unlike it looks. `datetime `also takes up 8 bytes of storage, with `datetime2(3)`, only 7 bytes are consumed (with full precision the same though, 8 bytes). These are the notable differences between the two.

This can be done by altering these two files I guess:
https://github.com/HangfireIO/Hangfire/blob/5b696d4174e13c3dd9489cc6a863d3417c632e31/src/Hangfire.SqlServer/DefaultInstall.sql
https://github.com/HangfireIO/Hangfire/blob/5b696d4174e13c3dd9489cc6a863d3417c632e31/src/Hangfire.SqlServer/Install.sql

MS documentation:
https://docs.microsoft.com/en-us/sql/t-sql/data-types/datetime2-transact-sql

Start by comparing the timestamp column definitions in src/Hangfire.SqlServer/DefaultInstall.sql and src/Hangfire.SqlServer/Install.sql. Update the schema definitions consistently to use the requested datetime2 precision, then verify that both installation scripts produce matching timestamp types.

Written by the indexing model from the issue text.