Make date the default field in frontmatter

[PhilippeduPreez]

closes #445

Summary

• Uses date as default frontmatter field and uses created field if date is not found

Changes

• Blog layout components updated to use date instead of created
• date computed field added in contentlayer.config

Notes

• Since either created or date can be used, none of them is required, maybe there is a way to have at least one of them required?
• Tested that both date and created frontmatter fields works as expected

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 2136ebb76e58311ba623cb87ef85b20fc2a475a7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | -------------------- | ----- | | @flowershow/template | Patch | | @flowershow/core | Patch |

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[rufuspollock]

@khalilcodes could you review and approve if it looks good.

[rufuspollock]

@olayway let you review as well now you are around.