Support JSON values via env-vars for plugins enabled by default

[shai-ikko]

When using docker compose as shown in https://orthanc.uclouvain.be/book/users/docker-orthancteam.html, one easy way to configure the container is by setting environment variables. The documentation even gives examples of plugins configured by environment vars with JSON values, set in docker-compose.yml using a syntax such as

       # ...
       environment:
            # ...
            ORTHANC__WORKLISTS: |
                {
                    "Enable": true,
                    "FilterIssuerAet": false,
                    "SaveInOrthancDatabase": true
                }

This works for most plugins, but fails for plugins enabled by default like OE2, because configurator.py tries to merge the configuration with the default, before parsing the JSON. As a result, if you set ORTHANC__ORTHANC_EXPLORER2 to a JSON value, you get an exception in the container startup:

Traceback (most recent call last):
  File "/startup/generateConfiguration.py", line 72, in <module>
    configurator.mergeConfigFromDefaults(moveSoFiles=True)
  File "/startup/configurator.py", line 182, in mergeConfigFromDefaults
    self._mergeConfigFromDefaults(pluginDefaultConfig, pluginName)
  File "/startup/configurator.py", line 157, in _mergeConfigFromDefaults
    self.configuration = self._mergeConfigs(first=self.configuration, second=config, secondSource="defaults:" + defaultsGroup, jsonPath=JsonPath(), overwrite=False)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/startup/configurator.py", line 130, in _mergeConfigs
    self._mergeConfigs(first[k], second[k], secondSource, keyPath, overwrite)
  File "/startup/configurator.py", line 144, in _mergeConfigs
    first[k] = v
    ~~~~~^^^
TypeError: 'str' object does not support item assignment

The image in question is the current orthancteam/orthanc; I can only see the tag "latest" but it says

"Created": "2025-12-15T10:04:38.367049234Z",