fix(agent-detail): fix the language code in the payload

[pratimasakinala]

Changes

1. Fixes the language code that is set to the dynamicContent key by setting it to the languageCode variable in the component

Approach

The languageCode local variable is set to the language for which a translation is being added or the default app language. So utilizing it as part of the payload works best.

Testing Steps

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1. Login & go to Agent list view.
2. Create/Update a record.
3. Click on the submit button & check the network tab to view the payload. It should look like:

  body: {
    "fullName": "",
      ...
      "dynamicContent": {
        "en-US": {
          "description": ""
        }
      }
  }

4. Attempt to add a translation for any language.
5. Submit the form & verify that the payload looks like the above with the language-code matching that in the route.
6. Change the language selection from the navigation dropdown. Submit any of the above-mentioned forms and verify that the language code in the payload is still the app default language (en-US in this case).

Closes #318

[goseinthemachine]

Like how small this PR is.