Changes

Adds a dynamic Search page (/{locale}/search/[?query={query}]) with a search form and list of search results with matches (highlights).
Adds Search results HTML partial endpoint /{locale}/search/results.partial/?query={query}.
Adds Search API endpoint with required parameters /api/search?locale={locale}&query={query} and optional fuzzy={'true'|'1'|'false'|'0'} (defaults to true).
Search results link to matching pages using Text fragments (#:~:text={query}) so browsers can highlight and scroll to the query.
Uses DatoCMS Site Search under the hood, which does the indexing and provides an API to get search results.
Excludes non-main content (site header and site footer) from being indexed to prevent them showing up in every search result.
Adds a catch all API endpoint (pages/api/[...notFound].ts) so any API route not found returns a 404 JSON response rather than a 404 HTML page.
Adds OpenSearch support, so browsers support 'tab to search'.
Adds script to download DatoCMS site data to src/lib/site.json so it can be used in search and seo related files (and for other features in the future).

Associated issue

Resolves #23

Open preview link
Navigate to search (in header) (/en/search/)
Enter a search query (like 'heading') (or 'astro' if searching on /nl/search/)
Review the search results
Play around with the search parameter in the URL, try a very short one (1 or 2 characters)
Play around with the JSON endpoint: /api/search?locale=en&query=heading.
Play around with the HTML partial endpoint: /en/search/results.partial/?locale=en&query=heading.
Read docs/search.md to find out more.

[x] I have performed a self-review of my own code
[x] I have made sure that my PR is easy to review (not too big, includes comments) 🤷 bit big, included docs.
~~I have added/updated tests to prove that my feature works (if not possible please explain why)~~
[x] I have made changes to the README and if the change affects the project setup (npm commands changed, new service added, environmental variable added)
~~I have added a decision log entry if the change affects the architecture or changes a significant technology~~
[x] I have notified a reviewer

Latest commit:	`e4f62bc`
Status:	✅ Deploy successful!
Preview URL:	https://7e9c2422.head-start.pages.dev
Branch Preview URL:	https://feat-search.head-start.pages.dev