docs(cli): document minimal NodeJS support

[vmasek]

closes #864

• add minimal node of 20 to engine of the @code-pushup/cli package.json
• add badge to the Readme
• fix bump node version in the example CI action to v22 and update the actions used to v4 from deprecated v3

New badge on README

[github-actions]

Code PushUp

🥳 Code PushUp report has improved – compared current commit 33306b0 with previous commit 018c1f1.

🕵️ See full comparison in Code PushUp portal 🔍

🏷️ Categories

🏷️ Category	⭐ Previous score	⭐ Current score	🔄 Score change
Performance	🔴 48	🟡 52
Code coverage	🟢 90	🟢 90	–
Security	🟡 62	🟡 62	–
Updates	🟡 84	🟡 84	–
Accessibility	🟢 92	🟢 92	–
Best Practices	🟢 100	🟢 100	–
SEO	🟡 61	🟡 61	–
Type Safety	🟢 100	🟢 100	–
Bug prevention	🟢 100	🟢 100	–
Miscellaneous	🟢 100	🟢 100	–
Code style	🟢 100	🟢 100	–
Documentation	🔴 23	🔴 23	–

👍 1 group improved, 👍 5 audits improved, 14 audits changed without impacting score

🗃️ Groups

🔌 Plugin	🗃️ Group	⭐ Previous score	⭐ Current score	🔄 Score change
Lighthouse	Performance	🔴 48	🟡 52

20 other groups are unchanged.

🛡️ Audits

🔌 Plugin	🛡️ Audit	📏 Previous value	📏 Current value	🔄 Value change
Lighthouse	Speed Index	🟥 6.8 s	🟥 5.9 s
Lighthouse	Largest Contentful Paint	🟨 3.7 s	🟨 3.5 s
Lighthouse	First Contentful Paint	🟥 3.0 s	🟨 2.8 s
Lighthouse	Time to Interactive	🟥 14.1 s	🟥 14.0 s
Lighthouse	Total Blocking Time	🟥 6,090 ms	🟥 4,330 ms
Lighthouse	Avoids enormous network payloads	🟩 Total size was 1,840 KiB	🟩 Total size was 1,829 KiB
Lighthouse	Minimizes main-thread work	🟥 19.1 s	🟥 16.6 s
Lighthouse	JavaScript execution time	🟥 8.6 s	🟥 7.8 s
Lighthouse	Eliminate render-blocking resources	🟥 Potential savings of 310 ms	🟥 Potential savings of 930 ms
Lighthouse	Max Potential First Input Delay	🟥 2,550 ms	🟥 2,040 ms
Lighthouse	Uses efficient cache policy on static assets	🟨 29 resources found	🟨 29 resources found
Lighthouse	Reduce unused CSS	🟥 Potential savings of 67 KiB	🟥 Potential savings of 67 KiB
Lighthouse	Initial server response time was short	🟩 Root document took 450 ms	🟩 Root document took 310 ms
Lighthouse	Metrics	🟩 100%	🟩 100%
Lighthouse	Server Backend Latencies	🟩 130 ms	🟩 170 ms
Lighthouse	Network Round Trip Times	🟩 60 ms	🟩 30 ms
Lighthouse	Avoids an excessive DOM size	🟥 2,156 elements	🟥 2,160 elements
JS Packages	Outdated NPM prod dependencies.	🟨 13 outdated package versions (3 major, 8 minor, 2 patch)	🟨 15 outdated package versions (3 major, 8 minor, 4 patch)
JS Packages	Vulnerabilities for NPM dev dependencies.	🟥 28 vulnerabilities (8 critical, 9 high, 9 moderate, 2 low)	🟥 29 vulnerabilities (8 critical, 9 high, 10 moderate, 2 low)

586 other audits are unchanged.