admin: accept a list of collections in the task collection filter (#10953)

The collection filter was parsed twice with two syntaxes: the master-side
volume listing compiled the whole string as one regex, while EC encode and
EC balance detection split it on commas and matched each entry as a
wildcard. A volume had to pass both, so "collection-a,collection-b" matched
nothing (no collection is named that), and the ALL_COLLECTIONS sentinel,
which the master side skips, dropped every volume at the task side.

Parse it once, in one place: a comma-separated list where an entry is a
name with optional * and ? wildcards, or a regex when it carries regex
syntax. A regex entry now has to match the whole name unless it anchors
itself, so listing a collection no longer picks up its longer namesakes.

weed/command/scaffold/admin.toml

@@ -57,7 +57,8 @@
 # scan_interval_seconds = 3600
 # max_concurrent = 1
 # min_size_mb = 30
-# only process volumes from this collection ("" = all collections)
+# only process volumes from these collections, comma separated, "*" and "?" wildcards
+# and regex patterns allowed ("" = all collections)
 # collection_filter = ""
 # disk tags preferred for shard placement
 # preferred_tags = ["fast", "ssd"]