Add Indent Option to Output Formats

[JoeyShapiro]

Description

It would be nice if the syft package allowed for pretty printing SBOMs with custom indenting. The default for most formats is only 1 space, but I personally use a tab.

This change is in the works, but I wanted to bring attention to it because I have a few issues.

• the cyclone formats use a separate encoder package, that do not allow setting the indent
  • I can make a PR and do the changes to that package, but it would require a bit more coordination.
• Some formats do not have a Pretty option.
  • I can add an Indent option, but I feel like I should add a Pretty option while I'm at it. Unless there is a reason they do not have a Pretty option
  • But adding an Indent option without a Pretty option feels wrong for some reason

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have added unit tests that cover changed behavior
• I have tested my code in common scenarios and confirmed there are no regressions
• I have added comments to my code, particularly in hard-to-understand sections

[kzantow]

we should default this to either 2 or 4 spaces, probably.

[JoeyShapiro]

that's fine by me. I was just copying the default from what it was before. I think the rest of the code uses 2, so I will do that