feat(): add appId into algoliaConfig

[atroncy]

Motivation

Allow user to add their own appId into algolia configuration.
See the issue 465

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

• Do not change siteConfig.js
  • Run yarnpkg start from ../website
  • Make sure search work as before
• Add appId into algolia config in siteConfig.js,
  • Run yarnpkg start from ../website
  • Make sure search work and effectively use given appId (note i it did my own set of apiKey/appId for this test)

Note i did also ran yarn jest and yarn prettier.

Related PRs

Not related to any pr.

[JoelMarcey]

This looks good to me thanks!

[JoelMarcey]

@atroncy Thank you! I will merge this.

I will add the documentation for the Algolia fields in another commit.