Fix RDBMS filter construction for applications and flags

* Add a new byFlag resource filter feature to support filtering
  using flags.
  False by default since only system applications use it.
* Add filter definitions to flag pkg resource.
* Add support for using []string inside byValue filters.

codegen/assets/templates/gocode/store/rdbms/filters.go.tpl

@@ -52,6 +52,10 @@ func {{ .expIdent }}Filter(f {{ .goFilterType }})(ee []goqu.Expression, _ {{ .go
 		if val := strings.TrimSpace(f.{{ .expIdent }}); len(val) > 0 {
 			ee = append(ee, goqu.C({{ printf "%q" .storeIdent }}).Eq(f.{{ .expIdent }}))
 		}
+		{{ else if eq .goType "[]string" }}
+		if ss := trimStringSlice(f.{{ .expIdent }}); len(ss) > 0 {
+			ee = append(ee, goqu.C({{ printf "%q" .storeIdent }}).In(ss))
+		}
 		{{ else if eq .goType "bool" }}
 		if f.{{ .expIdent }} {
 			ee = append(ee, goqu.C({{ printf "%q" .storeIdent }}).IsTrue())
@@ -76,6 +80,12 @@ func {{ .expIdent }}Filter(f {{ .goFilterType }})(ee []goqu.Expression, _ {{ .go
 	}
 	{{ end }}
 
+	{{ if .filter.byFlag }}
+	if len(f.FlaggedIDs) > 0 {
+		ee = append(ee, goqu.I("id").In(f.FlaggedIDs))
+	}
+	{{ end }}
+
 	{{ if .filter.query }}
 	if f.Query != "" {
 		ee = append(ee, goqu.Or(
@@ -89,3 +99,14 @@ func {{ .expIdent }}Filter(f {{ .goFilterType }})(ee []goqu.Expression, _ {{ .go
 	return ee, f, err
 }
 {{ end }}
+
+// trimStringSlice is a utility to trim all of the string slice elements and omit empty ones
+func trimStringSlice(in []string) []string {
+	out := make([]string, 0, len(in))
+	for _, s := range in {
+		if t := strings.TrimSpace(s); len(t) > 0 {
+			out = append(out, t)
+		}
+	}
+	return out
+}

codegen/schema/resource.cue

@@ -42,6 +42,9 @@ import (
 		// filtering by label
 		labels:   bool | *true
 
+		// filtering by flag
+		flags:   bool | *false
+
 		// support pagination
 		paging:   bool | *true
 

codegen/server.store.cue

@@ -44,6 +44,7 @@ _StoreResource: {
 			// @todo this should be pulled from the struct
 			"byValue":      [ for name in res.filter.byValue {res.filter.struct[name]}]
 			"byLabel": res.features.labels
+			"byFlag":  res.features.flags
 		}
 
 		auxIdent:  "aux\(expIdent)"