Add support for quoted environment variables

Environment variables with spaces in them must be quoted, otherwise
`make run` will report `command not found`:

```
$ grep DEYE_HA_PLUGIN_INVERTER_MODEL config.env
DEYE_HA_PLUGIN_INVERTER_MODEL=SUN300G3 EU 230

$ make run
config.env: line 49: EU: command not found
2024-06-10 21:13:44,180 - DeyeDaemon - INFO - Please help me build the list of compatible inverters. kbialek#41
2024-06-10 21:13:44,190 - DeyePluginLoader - INFO - Loading plugin: 'deye_plugin_ha_discovery'
2024-06-10 21:13:44,191 - DeyeConnectorFactory - INFO - Creating Modbus/TCP Logger connector
[...]
```

With the quotation marks, the environment variables in Docker are
slightly different:

**Setup:**

```
$ grep DEYE_HA_PLUGIN_INVERTER_MODEL config.env
DEYE_HA_PLUGIN_INVERTER_MODEL="SUN300G3 EU 230"
```

**Unix Shell and local  Python**

```
$ strings /proc/<pid>/environ | grep DEYE_HA_PLUGIN_INVERTER_MODEL
DEYE_HA_PLUGIN_INVERTER_MODEL=SUN300G3 EU 230
```

**Docker**

```
$ strings /proc/<pid>/environ | grep DEYE_HA_PLUGIN_INVERTER_MODEL
DEYE_HA_PLUGIN_INVERTER_MODEL="SUN300G3 EU 230"
```

This change addresses the different behavior of Docker compared to a
Unix shell and removes single and double quotes only if they are the
first and last character of the string.

The functionality was added to `DeyeEnv.integer()` and
`DeyeEnv.boolean()` for the sake of convenience to avoid problems with
quotes that may occur later.

src/deye_config.py

@@ -35,9 +35,19 @@ def process(self, msg, kwargs):
 
 
 class DeyeEnv:
+    @staticmethod
+    def unquote(value: str) -> str:
+        """Remove single and double quotes at the beginning and the end"""
+        if value and value[0] == '"' and value[-1] == '"':
+            value = value[1:-1]
+        elif value and value[0] == "'" and value[-1] == "'":
+            value = value[1:-1]
+        return value
+
     @staticmethod
     def integer(env_var_name: str, default_value: int = None) -> int:
         value = os.getenv(env_var_name)
+        value = DeyeEnv.unquote(value)
         if value:
             try:
                 return int(value)
@@ -51,6 +61,7 @@ def integer(env_var_name: str, default_value: int = None) -> int:
     @staticmethod
     def boolean(env_var_name: str, default_value: bool = None) -> bool:
         value = os.getenv(env_var_name)
+        value = DeyeEnv.unquote(value)
         if value and value == "true":
             return True
         elif value and value == "false":
@@ -67,6 +78,7 @@ def boolean(env_var_name: str, default_value: bool = None) -> bool:
     @staticmethod
     def string(env_var_name: str, default_value: str = None) -> str | None:
         value = os.getenv(env_var_name)
+        value = DeyeEnv.unquote(value)
         if value:
             return value
         elif default_value is not None: