feat: add OpenGraph image, tags, published/modified time, canonical URL support

[JoeyC-Dev]

Type of change

• Bug fix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (please describe):

Checklist

• I have read the CONTRIBUTING document.
• I have checked to ensure that this Pull Request is not for personal changes.
• I have performed a self-review of my own code.
• My changes generate no new warnings.

Related Issue

Resolves: #323
Resolves: #114

Changes

• Add OG image, tags, published/modified time support (search engine will be able to know when you change the content)
• Add canonical URL support (avoid the past indexing issue with '/post/slug' or '/post/slug/', even though the issue was being addressed in another way)

How To Test

• Add a cover to the article and check if og:image and twitter:image are included.
• Check if article:published_time, article:modified_time (optional), article:tag is in the header.
• Check if rel="canonical" is in the header.

Screenshots (if applicable)

Tested here: https://www.opengraph.xyz

Results from Bing:

You can tell that newly indexed pages (result 2 & 3) now have their formatted date read from the Open Graph properties.

Additional Notes

This is the follow-up PR to: #66

I see two previous PRs for OG image generators, but before considering the generator, a simple basic implementation is okay for use, honestly.

Update: I changed my mind. I want to complete what I haven't finished in #66 once and for all, so I made new commits.

[vercel]

@JoeyC-Dev is attempting to deploy a commit to the zephyirdgmailcom's projects Team on Vercel.

A member of the Team first needs to authorize it.

[JoeyC-Dev]

Hi lint/complexity/noUselessUndefinedInitialization in GitHub Actions/quality,

Do you know if removing | undefined = undefined does cause an error like below?