website: improve URL preview metadata

[alexandear]

When sharing links to the documentation on Slack or Discord, the URL preview often shows low-value text.

For example, when sharing https://golangci-lint.run/docs/linters/configuration/ or https://golangci-lint.run/docs/formatters/configuration/ the preview displays the first few linters or formatters from the page content:

It would be great to improve these first few sentences and display useful info (e.g., short page description).