Aggregator: ignore advisories by given patterns (#421)

* Ignore advisories in checker.

* Rename config.check to config.prepare to make symmerical to other tools.

* Add ignore patterns to aggreagtor.

* Clarified docs on where and how to use ignorepattern for aggregator

---------

Co-authored-by: JanHoefelmeyer <hoefelmeyer.jan@gmail.com>

cmd/csaf_aggregator/main.go

@@ -45,7 +45,7 @@ func lock(lockFile *string, fn func() error) error {
 func main() {
 	_, cfg, err := parseArgsConfig()
 	options.ErrorCheck(err)
-	options.ErrorCheck(cfg.check())
+	options.ErrorCheck(cfg.prepare())
 	p := processor{cfg: cfg}
 	options.ErrorCheck(lock(cfg.LockFile, p.process))
 }