Fix generating environment variables from job configurations for multi-level nesting

[alaydshah]

If the configuration path for config_sub_key is as follows:

config_parent_key:
    config_sub_key: config_sub_key_value

Then the equivalent environment variable should be as follows:
FEDML_ENV_uppercase($config_parent_key)_uppercase($config_sub_key)

This approach should be implemented recursively for any depth of nesting. However, there is currently a bug for nesting beyond two layers where it skips earlier level's config keys.

Example Job yaml multi-level nesting:

level-1:
  level-2a:
    level-3a: $3000   
    level-3b: A100-80G

  level-2b: $3000
  level-2c: A100-80G

Before this fix / Current Bug:

env_name_value_map

'FEDML_ENV_LEVEL-2A_LEVEL-3A' = '$3000'
'FEDML_ENV_LEVEL-2A_LEVEL-3B' = 'A100-80G'
'FEDML_ENV_LEVEL-1_LEVEL-2B' = '$3000'
'FEDML_ENV_LEVEL-1_LEVEL-2C' = 'A100-80G'

After this fix:

env_name_value_map

'FEDML_ENV_LEVEL-1_LEVEL-2A_LEVEL-3A' = '$3000'
'FEDML_ENV_LEVEL-1_LEVEL-2A_LEVEL-3B' =  'A100-80G'
'FEDML_ENV_LEVEL-1_LEVEL-2B' = '$3000'
'FEDML_ENV_LEVEL-1_LEVEL-2C' = 'A100-80G'