fix: browser header showing null and replace authn with Authentication

[hinakhadim]

Description

When accessing Authn MFE for the first time it shows "Auth | null" in the browser header. This PR will fix If process.env.SITE_NAME is not available it will show “Authentication” otherwise show “Authentication | {site_name}”. This bug (#1158) has been fixed in #1168 but still not resolve. As process.env.SITE_NAME is null but in index.html, it assumes null as a string value and passed the condition which is expected to be failed. As a result, still showing Authn | null. Moreover, in this PR, I have replaced Authn with the Authentication as suggested here.

How Has This Been Tested?

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Before	After

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.32%. Comparing base (ca42f38) to head (97b270c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1185   +/-   ##
=======================================
  Coverage   84.32%   84.32%           
=======================================
  Files         127      127           
  Lines        2398     2398           
  Branches      680      680           
=======================================
  Hits         2022     2022           
  Misses        356      356           
  Partials       20       20           

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[arbrandes]

I would've approved the fix, too, but at some point we should just start using react-helmet everywhere, like other MFEs already do.