feat(cache): allow async getKey option in cache utils

[MiniDigger]

🔗 Linked issue

#875

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Example:

export default defineCachedEventHandler(async () => {
  await new Promise((resolve) => setTimeout(resolve, 1000));
  console.log("event called")
  return `Response generated at ${new Date().toISOString()} (took 1 second)`;
}, {
  maxAge: 600,
  getKey: async (e) => {
    await new Promise((resolve) => setTimeout(resolve, 500));
    console.log("getKey called")
    return e.node.req.url
  }
});

usecase further explained in #875

I am not sure where this could be mentioned in the docs, should be obvious by the typing that promises/async are allowed?

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #878 (4a9ba0d) into main (f5a5a8e) will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #878      +/-   ##
==========================================
- Coverage   67.42%   67.34%   -0.09%     
==========================================
  Files          59       59              
  Lines        5852     5852              
  Branches      633      632       -1     
==========================================
- Hits         3946     3941       -5     
- Misses       1897     1901       +4     
- Partials        9       10       +1     

Impacted Files	Coverage Δ
src/rollup/config.ts	91.66% <0.00%> (-0.93%)	⬇️
src/utils/index.ts	52.35% <0.00%> (-0.53%)	⬇️

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[pi0]

Thanks!

[MiniDigger]

thank you for the awesome project and speed reviews! 🚀