Blogging Prompts: Add prompt metadata to prompt posts

[wargcm]

See: #18429
WPKit PR: wordpress-mobile/WordPressKit-iOS#515

Description

Adds prompt metadata to posts when answering a prompt in order to track if it has been answered.

Testing

Note: There's an existing caching issue where the prompt data will not update after answering the prompt. A temporary change is needed in BloggingPromptsService.swift:

// BloggingPromptsService.swift

    func todaysPrompt(success: @escaping (BloggingPrompt?) -> Void,
                      failure: @escaping (Error?) -> Void) {
//        guard localTodaysPrompt == nil else {
//            success(localTodaysPrompt)
//            return
//        }

        fetchTodaysPrompt(success: success, failure: failure)
    }

To test:

• Enable bloggingPrompts feature flag in FeatureFlag.swift
• Launch the app and sign in if necessary
• Select a public site
• Navigate to the 'My Site' tab
• Tap on 'Answer Prompt'
• In the editor, publish the post publicly
• After the post is uploaded, trigger the todaysPrompt (switch to another blog and then back, this should call the configure method on the dashboard card which calls todaysPrompt)
• Verify the prompt is marked as 'Answered' and the answer count is updated

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes in Jetpack from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr18808-6f817e2 on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[wpmobilebot]

You can test the changes in WordPress from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr18808-6f817e2 on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[alpavanoglu]

Hey, following the testing steps, I wasn't able to trigger todaysPrompt. Also even though I've answered the prompt the counter for it does not seem to increment.
Is there a specific way to make the todaysPrompt appear?

[wargcm]

@alpavanoglu I thought that navigating back would trigger it but I was mistaken. I realize now those steps are incorrect after working on the prompt caching issue.

One way that should trigger the fetchPrompts call is switching blogs. I'll update the test instructions. Sorry about that!

[peril-wordpress-mobile]

	Warnings
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

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