Enhance search performance of algolia plugin

[KevinEyo1]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• DevOps
• Improve developer experience
• Others, please explain:

Overview of changes:
Resolves #2015
Added snippet to the head of your website when using Algolia for performance optimization.

Anything you'd like to highlight/discuss:

Testing instructions:

Proposed commit message: (wrap lines at 72 characters)
Enhance search performance. It would allow user to make the
first query faster, especially on mobile, making their user
experience better.

Let's hint the browser that the website will load data from
Algolia, allowing it to preconnect to the DocSearch cluster.

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

---

Reviewer checklist:

Indicate the SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a265c73) 48.87% compared to head (4272f81) 48.87%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2406   +/-   ##
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  Coverage   48.87%   48.87%           
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  Files         124      124           
  Lines        5238     5238           
  Branches     1109     1109           
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  Hits         2560     2560           
  Misses       2371     2371           
  Partials      307      307           

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[kaixin-hc]

In my testing, this seems to work and preview links SEEM to load faster as opposed to when this is not there (comparing the netlify preview on master and on this PR)

It would be great if you could show any testing you've done to verify this PR!

[yucheng11122017]

LGTM!

[kaixin-hc]

@all-contributors please add @KevinEyo1 for code

[allcontributors]

@kaixin-hc

I've put up a pull request to add @KevinEyo1! 🎉