[24.1] Make all fields optional for HelpForumPost

[davelopez]

Fixes #18827

Unfortunately, the OpenAPI schema for the /search.json route in Discourse (https://docs.discourse.org/openapi.json) does not specify the proper type for the posts array in the response.

...
"properties": {
    "posts": {
        "type": "array",
        "items": {}
    },
    "users": {
        "type": "array",
        "items": {}
    },
    "categories": {
        "type": "array",
        "items": {}
    },
    "tags": {
        "type": "array",
        "items": {}
    },
    "groups": {
        "type": "array",
        "items": {}
    }
...

We can try to infer it from /posts.json but there, seem to be no required properties at all, which is also strange.

I made all the properties except for the id optional in case more cases like these exist.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Thanks!