feat: make portal-client dependency optional

[hanna-skryl]

Closes #474

• Make @code-pushup/portal-client an optional peer dependency in the @code-pushup/core package.
• Update the core package to use dynamic imports for @code-pushup/portal-client.
• Add a utility function to handle the loading of the portal client.
• Update the installation instructions to guide users on omitting optional dependencies, including details for npm, pnpm, and yarn setups.

[github-actions]

Code PushUp

🤨 Code PushUp report has both improvements and regressions – compared target commit 01f02b6 with source commit c420a68.

🕵️ See full comparison in Code PushUp portal 🔍

🏷️ Categories

🏷️ Category	⭐ Previous score	⭐ Current score	🔄 Score change
Performance	🟡 52	🔴 43
Code coverage	🟢 90	🟢 90
Custom checks	🟡 67	🟡 67	–
Security	🟡 82	🟡 82	–
Updates	🟡 77	🟡 77	–
Accessibility	🟢 91	🟢 91	–
Best Practices	🟢 100	🟢 100	–
SEO	🟡 61	🟡 61	–
Bug prevention	🟢 100	🟢 100	–
Code style	🟢 99	🟢 99	–

👎 2 groups regressed, 👍 2 audits improved, 👎 6 audits regressed, 11 audits changed without impacting score

🗃️ Groups

🔌 Plugin	🗃️ Group	⭐ Previous score	⭐ Current score	🔄 Score change
Lighthouse	Performance	🟡 52	🔴 43
Code coverage	Code coverage metrics	🟢 90	🟢 90

18 other groups are unchanged.

🛡️ Audits

🔌 Plugin	🛡️ Audit	📏 Previous value	📏 Current value	🔄 Value change
Lighthouse	Largest Contentful Paint	🟨 3.2 s	🟥 4.2 s
Lighthouse	First Contentful Paint	🟥 3.2 s	🟥 3.6 s
Lighthouse	First Meaningful Paint	🟨 3.2 s	🟨 3.6 s
Lighthouse	Speed Index	🟥 6.4 s	🟥 6.6 s
Lighthouse	Time to Interactive	🟥 19.6 s	🟥 17.8 s
Code coverage	Branch coverage	🟨 85.4 %	🟨 85.3 %
Code coverage	Line coverage	🟩 91.5 %	🟩 91.5 %
Code coverage	Function coverage	🟩 92.4 %	🟩 92.4 %
Lighthouse	Avoids enormous network payloads	🟩 Total size was 1,823 KiB	🟩 Total size was 1,818 KiB
Lighthouse	Minimizes main-thread work	🟥 24.3 s	🟥 22.4 s
Lighthouse	Total Blocking Time	🟥 9,650 ms	🟥 7,920 ms
Lighthouse	Metrics	🟩 100%	🟩 100%
Lighthouse	Max Potential First Input Delay	🟥 4,900 ms	🟥 3,220 ms
Lighthouse	JavaScript execution time	🟥 11.8 s	🟥 11.0 s
Lighthouse	Eliminate render-blocking resources	🟥 Potential savings of 1,270 ms	🟥 Potential savings of 1,490 ms
Lighthouse	Uses efficient cache policy on static assets	🟨 27 resources found	🟨 27 resources found
Lighthouse	Server Backend Latencies	🟩 150 ms	🟩 220 ms
Lighthouse	Network Round Trip Times	🟩 20 ms	🟩 60 ms
Lighthouse	Initial server response time was short	🟩 Root document took 410 ms	🟩 Root document took 380 ms

494 other audits are unchanged.