fix: config to support keys with special values (#9304)

This PR adds context-based `k=v` splits based
on the sub-system which was obtained, if the
keys are not provided an error will be thrown
during parsing, if keys are provided with wrong
values an error will be thrown. Keys can now
have values which are of a much more complex
form such as `k="v=v"` or `k=" v = v"`
and other variations.

additionally, deprecate unnecessary postgres/mysql
configuration styles, support only

- connection_string for Postgres
- dsn_string for MySQL

All other parameters are removed.

pkg/madmin/config-kv-commands.go

@@ -78,7 +78,7 @@ func (adm *AdminClient) SetConfigKV(ctx context.Context, kv string) (err error)
 }
 
 // GetConfigKV - returns the key, value of the requested key, incoming data is encrypted.
-func (adm *AdminClient) GetConfigKV(ctx context.Context, key string) (Targets, error) {
+func (adm *AdminClient) GetConfigKV(ctx context.Context, key string) ([]byte, error) {
 	v := url.Values{}
 	v.Set("key", key)
 
@@ -100,10 +100,5 @@ func (adm *AdminClient) GetConfigKV(ctx context.Context, key string) (Targets, e
 		return nil, httpRespToErrorResponse(resp)
 	}
 
-	data, err := DecryptData(adm.getSecretKey(), resp.Body)
-	if err != nil {
-		return nil, err
-	}
-
-	return ParseSubSysTarget(data)
+	return DecryptData(adm.getSecretKey(), resp.Body)
 }