[bug] Not effective version of mysql56

[hustjieke]

Describe the problem

The mysql version will never be mysql56:

166 // buildXenonConf build a config file for xenon.
167 func (cfg *Config) buildXenonConf() []byte {
               ....
               ....
171 
172         version := "mysql80"
173         if cfg.MySQLVersion.Major == 5 {
174                 if cfg.MySQLVersion.Minor == 6 {
175                         version = "mysql56"
176                 } else {
177                         version = "mysql57"
178                 }
179         }

In GetMySQLVersion, no matter what mysql version is, it always be 5.7 here.

113 // GetMySQLVersion returns the MySQL server version.
114 func (c *Cluster) GetMySQLVersion() string {
115         version := c.Spec.MysqlVersion
116         // lookup for an alias, usually this will solve 5.7 to 5.7.x
117         if v, ok := utils.MySQLTagsToSemVer[version]; ok { 
118                 version = v
119         }       
120                 
121         if _, ok := utils.MysqlImageVersions[version]; !ok {
122                 version = utils.MySQLDefaultVersion
123         }       
124         
125         return version
126 }

To Reproduce

Expected behavior

Environment:

• RadonDB MySQL version: