feat: extract client auth code in a library

[cromoteca]

Adds a NPM module which extracts some existing code from auth support in Starter and SSO Kit.

This will allow to simplify the creation of new applications.

Closes #1235

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (7722b7a) 96.70% compared to head (105f59c) 96.70%.
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1264   +/-   ##
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  Coverage   96.70%   96.70%           
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  Files          14       14           
  Lines        1698     1698           
  Branches      144      144           
=======================================
  Hits         1642     1642           
  Misses         56       56           

Flag	Coverage Δ
unittests	96.70% <ø> (ø)

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[Artur-]

Some random initial comments about the module and not at all about the actual content. I had to do most of these changes to the react-grid module also

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
0.0% Duplication

[vaadin-bot]

This ticket/PR has been released with Hilla 2.3.0.alpha5 and is also targeting the upcoming stable 2.3.0 version.

[tarekoraby]

Does this imply changes to the docs? Did we start planning this?

[cromoteca]

Probably yes. The docs explain how to implement from scratch. It is probably easier to use the new package. But the first thing to do is to use this package in the Start (pre-release version).

[cromoteca]

Ping @platosha