Update Install.sql to alter tables instead of creating them on every run.

[agabuza]

Every time running .UseSQLiteStorage(ConnectionString, options) it attempts to create Hangfire-related tables even if they already exist. This leads to sql-exception and failure.

[agabuza]

Proposing to use SQLite 3.3 IF NOT EXISTS statement which will ignore already created items and create missing. It can be used on both CONSTRAINS and TABLES which pretty much covers all cases.

[rocker8942]

This is already done in https://github.com/wanlitao/HangfireExtension/issues Have a look at.