Do not trigger BomSbtPlugin automatically

[ep-skolberg]

Fixes #210

[raboof]

While I appreciate this makes things slightly simpler in the case where you want to enable SBOMs for only a few subprojects, it makes things more complicated in the case where you want to enable SBOMs for all (sub)projects, which seems like the more common case.... I'm not sure this balances out.

Is it a strong convention among sbt plugins to only take effect when explicitly enabled?

[ep-skolberg]

While I appreciate this makes things slightly simpler in the case where you want to enable SBOMs for only a few subprojects, it makes things more complicated in the case where you want to enable SBOMs for all (sub)projects, which seems like the more common case.... I'm not sure this balances out.

Is it a strong convention among sbt plugins to only take effect when explicitly enabled?

Not sure about any conventions or what is the most common case.

I'm coming from a rather big mono repo project where we have dozens of modules that produce libraries, we use in differing combinations in very few application binaries.
As we do not publish libraries and only use them internally, there is no need for us to create SBOM's for those.

Before, I go and disable this one plugin 348 times (or so) ,I guess I would rather fork and build my own version, which again is a pain of a different kind.

[ep-skolberg]

This is just a proposal or an attempt to make my life easier. If this doesn't work for others, I will deal ;)

And I have no idea why the build is failing