Make Algolia optional

[donmhico]

I noticed that if the Algolia env vars are not set ( NEXT_PUBLIC_ALGOLIA_INDEX_NAME, NEXT_PUBLIC_ALGOLIA_APPLICATION_ID, NEXT_PUBLIC_ALGOLIA_SEARCH_ONLY_KEY ) the site doesn't load. I get this error

Server Error

Error: Error serializing `.algolia.indexName` returned from `getStaticProps` in "/".
Reason: `undefined` cannot be serialized as JSON. Please use `null` or omit this value.

In my own opinion, as a starter, I think the lesser we need to setup the better.

We can change this block of code

nextjs-wordpress-starter/api/algolia/connector.js

Lines 4 to 6 in 1ed3c99

	export const algoliaIndexName = process.env.NEXT_PUBLIC_ALGOLIA_INDEX_NAME
	export const algoliaSearchKey = process.env.NEXT_PUBLIC_ALGOLIA_SEARCH_ONLY_KEY
	export const algoliaAppId = process.env.NEXT_PUBLIC_ALGOLIA_APPLICATION_ID

to

// Define env vars.
export const algoliaIndexName = process.env.NEXT_PUBLIC_ALGOLIA_INDEX_NAME ?? null
export const algoliaSearchKey = process.env.NEXT_PUBLIC_ALGOLIA_SEARCH_ONLY_KEY ?? null
export const algoliaAppId = process.env.NEXT_PUBLIC_ALGOLIA_APPLICATION_ID ?? null

This change will make the Algolia related env vars optional, at least until the user actually wants to use the Algolia Search component.

[gregrickaby]

@donmhico I'm fine with this change. Submit a PR and I'll get it merged in.