Add support for MS SQL Server

[italolelis]

Add support for MS SQL Server as a storage option for the outboxer

[m4ver1k]

I would like to give this a try.

So I have to implement DataStore interface for MS SQL Server.

While looking for available drivers found go-mssqldb and gofreetds . The former being more popular in GitHub going with that.

[italolelis]

@m4ver1k sounds good, thanks for helping. Looking forward to see what you come up with.

[m4ver1k]

Using these to implement advisory locks

• sp-getapplock
• sp-releaseapplock

[m4ver1k]

@italolelis I was facing an issue with inserting nil type to a varbinary column and figured out the issue is with the driver I was using have raised a bug here.

denisenkom/go-mssqldb#530

[m4ver1k]

I will figure out a way around this or try with another driver.
Have implemented the DataStore interface for SqlServer. Tests are pending.
Should be able to wrap up this weekend.

[italolelis]

@m4ver1k Thanks a lot for the effort you are putting into this. I really appreciate it.
Looking forwards to the PR 👍