[feature] support configuring database caches (#1246)

* update config generator to support nested structs, add cache configuration options

* update envparsing test

* add cache configuration to config parse tests

* set cache configuration in testrig

* move caches to sub-cache "gts" namespace, update envparsing, add cache config docs to example config

Signed-off-by: kim <grufwub@gmail.com>

internal/config/state.go

@@ -41,8 +41,8 @@ func NewState() *ConfigState {
 	viper := viper.New()
 
 	// Flag 'some-flag-name' becomes env var 'GTS_SOME_FLAG_NAME'
-	viper.SetEnvPrefix("gts")
 	viper.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
+	viper.SetEnvPrefix("gts")
 
 	// Load appropriate named vals from env
 	viper.AutomaticEnv()
@@ -132,9 +132,13 @@ func (st *ConfigState) reloadToViper() {
 func (st *ConfigState) reloadFromViper() {
 	if err := st.viper.Unmarshal(&st.config, func(c *mapstructure.DecoderConfig) {
 		c.TagName = "name"
-		c.ZeroFields = true // empty the config struct before we marshal values into it
+
+		// empty config before marshaling
+		c.ZeroFields = true
 
 		oldhook := c.DecodeHook
+
+		// Use the TextUnmarshaler interface when decoding.
 		c.DecodeHook = mapstructure.ComposeDecodeHookFunc(
 			mapstructure.TextUnmarshallerHookFunc(),
 			oldhook,