feat(head): add structured-data support for seo.

[neoFelhz]

Contributing rules

• Fork the repo and create your branch from canary. Then be sure to put the canary branch as the target for your pull request.
• Please be sure to follow the contributing guidelines, especially for commit message
• Remove the Contributing rules part from this description
• Fill out the other parts from this description

If you don't do so, we might change your pull request's title and using squash to merge your changed.

What kind of change does this PR introduce? (check one with "x")

• Bug fix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

---

Description

I add structured-data support for seo.

I thought there might be something wrong if users have not configure their config file, so I add a switch in theme.head.structured_data .

---

Verification steps

I have already tested about it, and it works well!