fix: centralize edge functions feature flags

[eduardoboucas]

Summary

We have two different places where we need to send edge functions feature flags to Netlify Build. This PR centralises them.

[danez]

Good catch

[github-actions]

📊 Benchmark results

Comparing with d64c875

Package size: 249 MB

(no change)

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Legend

• T-23 (67e4e39): 247 MB
• T-22 (90a357d): 247 MB
• T-21 (d3be8a1): 247 MB
• T-20 (be5098e): 247 MB
• T-19 (fd7db45): 247 MB
• T-18 (57ee933): 247 MB
• T-17 (26c409d): 247 MB
• T-16 (38f548f): 247 MB
• T-15 (ff1eecb): 254 MB
• T-14 (990da12): 254 MB
• T-13 (869c5a8): 254 MB
• T-12 (62930d8): 254 MB
• T-11 (345ce9c): 254 MB
• T-10 (0041559): 254 MB
• T-9 (e65f97c): 254 MB
• T-8 (35123df): 254 MB
• T-7 (a49e5fc): 249 MB
• T-6 (6214768): 242 MB
• T-5 (acdcbb6): 242 MB
• T-4 (743b4d6): 242 MB
• T-3 (f9f45ed): 249 MB
• T-2 (22de9e2): 249 MB
• T-1 (d64c875): 249 MB
• T (current commit): 249 MB