Fix extra_vars bug in ansible.controller.ad_hoc_command

[jessicamack]

SUMMARY

Related #14481
We're currently submitting an OrderedDict to a CharField which is throwing a validation error on the serializer.
This PR converts the OrderedDict to a JSON string before submitting it.

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API

AWX VERSION

awx: 23.2.1.dev20+gcec6e1e93a.d20231018

ADDITIONAL INFORMATION

Before

PLAY [all] ************************************************************************************************************
TASK [Launch an ad hoc command] ***************************************************************************************
[WARNING]: You are running collection version 22.7.0 but connecting to AWX version 23.1.1.dev1+g8feeb5f1fa
fatal: [localhost]: FAILED! => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python3"}, "changed": false, "msg": "Failed to launch command, see response for details", "response": {"json": {"extra_vars": ["Not a valid string."]}, "status_code": 400}}
PLAY RECAP ************************************************************************************************************
localhost                  : ok=0    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0 

After

PLAY [all] ************************************************************************************************************
TASK [Launch an ad hoc command] ***************************************************************************************
[WARNING]: You are running collection version 22.7.0 but connecting to AWX version 23.1.1.dev1+g8feeb5f1fa
changed: [localhost] => {"ansible_facts": {"discovered_interpreter_python": "/usr/bin/python3"}, "changed": true, "id": 76, "status": "new"}
PLAY RECAP ************************************************************************************************************
localhost                  : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0    

[TheRealHaoLiu]

TASK [ad_hoc_command : Launch an Ad Hoc Command with extra_vars] ***************
task path: /home/runner/.ansible/collections/ansible_collections/awx/awx/tests/output/.tmp/integration/ad_hoc_command-0s_7_o2t-ÅÑŚÌβŁÈ/tests/integration/targets/ad_hoc_command/tasks/main.yml:75
Using module file /home/runner/.ansible/collections/ansible_collections/awx/awx/plugins/modules/ad_hoc_command.py
Pipelining is enabled.
<testhost> ESTABLISH LOCAL CONNECTION FOR USER: runner
<testhost> EXEC /bin/sh -c '/usr/bin/python3 && sleep 0'
changed: [testhost] => {
    "changed": true,
    "id": 3,
    "invocation": {
        "module_args": {
            "become_enabled": null,
            "controller_config_file": null,
            "controller_host": null,
            "controller_oauthtoken": null,
            "controller_password": null,
            "controller_username": null,
            "credential": "AWX-Collection-tests-ad_hoc_command-ssh-cred-UiZvdOKfOepLHwLS",
            "diff_mode": null,
            "execution_environment": null,
            "extra_vars": {
                "var1": "test var"
            },
            "forks": null,
            "interval": 2.0,
            "inventory": "Demo Inventory",
            "job_type": null,
            "limit": null,
            "module_args": null,
            "module_name": "ping",
            "request_timeout": null,
            "timeout": null,
            "validate_certs": null,
            "verbosity": null,
            "wait": true
        }
    },
    "status": "successful"
}

TASK [ad_hoc_command : assert] *************************************************
task path: /home/runner/.ansible/collections/ansible_collections/awx/awx/tests/output/.tmp/integration/ad_hoc_command-0s_7_o2t-ÅÑŚÌβŁÈ/tests/integration/targets/ad_hoc_command/tasks/main.yml:85
ok: [testhost] => {
    "changed": false,
    "msg": "All assertions passed"
}

confirmed that the new test is being ran in the CI and passes