followups to build webhook trigger secret references

[bparees]

Follow ups to:
#17314

• buildtriggercause includes the secret value partially masked. should not expose it at all: mask webhook secret value in builds #18389
• webhook trigger docs needs updating: document secretrefs for build webhook triggers openshift-docs#6552
• quickstarts need to be updated to use the new reference mechanism
• new-app needs to be updated to produce webhook triggers that use secret refs
• do we care about the clutter of secrets that will be left behind when people delete their buildconfigs? should we use GC to clean them up?

Unfortunately changes to new-app and the quickstarts won't be backwards compatible, so we can't change new-app until 3.10. Not sure when we'd want to change the quickstarts.

/cc @jim-minter

[bparees]

@jwforres is it going to cause you problems if we stop reporting the value of the secret used to trigger a build for builds triggered by a webhook?

[bparees]

(or if we just start reporting it as all asterisks)

[jwforres]

@bparees i dont see any refs to buildtriggercause in the console, so no dont think so

[openshift-bot]

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[bparees]

/remove-lifecycle stale
/lifecycle frozen