convert value to dictionary (#659)

#649 @stan-dot 

For the environment to work, it needed to be in dictionary from so a
string to dictionary conversion is needed. This was me playing with it.

You probably already working on it, the cli_value are all none unless
you assign them so pydantic keep complaining.

src/blueapi/config.py

@@ -1,3 +1,4 @@
+import ast
 import os
 from collections.abc import Mapping
 from enum import Enum
@@ -169,7 +170,7 @@ def use_values_from_env(self, prefix: str = "APP_") -> None:
             if key.startswith(prefix):
                 # Convert key to a config path-like structure
                 config_key = key[len(prefix) :].lower()
-                env_values[config_key] = value
+                env_values[config_key] = ast.literal_eval(value)
         self.use_values(env_values)
 
     def use_values_from_cli(self, cli_args: Any) -> None:
@@ -189,5 +190,6 @@ def load(self) -> C:
             pretty_error_messages = pretty_print_errors(exc.errors())
 
             raise InvalidConfigError(
-                f"Something is wrong with the configuration file:\n{pretty_error_messages}"
+                "Something is wrong with the configuration file:\n"
+                + f"{pretty_error_messages}"
             ) from exc