Add release functionality to build system

[mattysmith22]

Aims

Add the ability for the entire release process to be performed by scons, that includes

• Signing key generation
• PBO signing
• Exporting relevant files to an export folder
• Zipping said export folder ready for export to Github releases

How do you envision this feature being implemented?

Use of ${a3ToolsDir}\DSSignFile\DSCreateKey.exe <authorityName> to generate fresh key
Use of ${a3ToolsDir}\DSSignFile\DSSignFile.exe <privateKey> <pboToSign> to sign fresh key
Scons can zip here.

Reference material

scons.

[mattysmith22]

This is a long term thing I would like to do, it can wait