dev: cleanup config package (#1929)

* split config section into files.
* extract anonymous types.
* sort linters alphabetically.

pkg/config/severity.go

@@ -0,0 +1,18 @@
+package config
+
+const severityRuleMinConditionsCount = 1
+
+type Severity struct {
+	Default       string         `mapstructure:"default-severity"`
+	CaseSensitive bool           `mapstructure:"case-sensitive"`
+	Rules         []SeverityRule `mapstructure:"rules"`
+}
+
+type SeverityRule struct {
+	BaseRule `mapstructure:",squash"`
+	Severity string
+}
+
+func (s *SeverityRule) Validate() error {
+	return s.BaseRule.Validate(severityRuleMinConditionsCount)
+}