[confcom] Update default value for `--infrastructure-svn` to latest

[DomAyre]

It's been reported that using --infrastructure-svn doesn't work when generating policies from VN2 deployment templates.

We need to reproduce the issue and then fix.

Update the default value for minimum infrastructure SVN when the arg isn't specified to 4

[yonzhan]

Thank you for opening this issue, we will look into it.

[DomAyre]

Turns out the issue is already fixed and the users who reported it were on an older version.

However it is raised that the default value for infrastructure SVN should be the latest version, so I will repurpose this issue to cover updating the default in code

[DomAyre]

We want to wait for Tingmao Wang (@micromaomao) to confirm the testing with the new SVN all works before doing this