feat(seed): introduce scripts to generators so fern bot can build the SDKs

[armandobelardo]

This upgrades the generators sdk dep to expose generator scripts from FDR

Then this exposes a similar configuration from seed config to have authors specify scripts within each generator's seed.yml that is then run within the generated artifacts resultant repo

The idea here is that within CI on fern config repos we:

• Create a check per-generator
• That check runs fern generate --preview for the specific generator
• On the resultant preview repo, we run the checks outlined here (within the corresponding seed.yml)
• We complete the check with the appropriate status (attaching logs)
  • We link to a preview of the SDK change in Github within the check as well