gh-files-set: preserve user-managed files on terraform destroy

[Copilot]

github_repository_file always calls the GitHub delete API on destroy — lifecycle { ignore_changes = [content] } only suppresses content drift, it does not prevent file deletion. terraform destroy would wipe user-managed files from GitHub.

Changes

• main.tf: Replace github_repository_file.user_managed with terraform_data + local-exec provisioner

  • terraform_data has no built-in destroy action; without a when = destroy provisioner, terraform destroy removes the state entry only — the GitHub file is untouched
  • Provisioner calls PUT /repos/{owner}/{repo}/contents/{file} via curl + $GITHUB_TOKEN on create/re-provision
  • Respects overwrite_on_create: fetches current SHA and skips or updates accordingly
  • triggers_replace = [file, branch] — content drift is intentionally ignored; only path or branch change re-provisions
  • JSON-safe commit message encoding (python3 → sed fallback); jq → grep/sed fallback for SHA extraction; API errors surfaced to stderr

• README.md / docs/header.md: Document preserve-on-destroy behavior; add GITHUB_TOKEN env var requirement (same token as the provider); update resource table to terraform_data.user_managed

• _examples/basic/files.yaml: Remove invalid lifecycle: {} field; add a userManaged: true example entry

# Before — file is deleted on terraform destroy
resource "github_repository_file" "user_managed" {
  lifecycle { ignore_changes = [content] }
}

# After — state entry removed, GitHub file preserved
resource "terraform_data" "user_managed" {
  triggers_replace = [each.value.file, each.value.branch]
  provisioner "local-exec" { command = <<-EOT ... EOT }
  # no when = destroy provisioner
}

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