(core) Fix flyctl cleanup; move/copy scripts to support preview deploys in grist-core

Summary:
- Fly flyctl cleanup which has been failing; deleting volumes before app no longer seems needed
- Move fly-deploy and add workflow scripts to make fly preview work in grist-core too

Test Plan: Tested that previews still work in this repo; and tested with a copy in grist-core.

Reviewers: jarek

Reviewed By: jarek

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3928

buildtools/fly-template.toml

@@ -0,0 +1,46 @@
+app = "{APP_NAME}"
+kill_signal = "SIGINT"
+kill_timeout = 5
+processes = []
+
+[env]
+  APP_DOC_URL="https://{APP_NAME}.fly.dev"
+  APP_HOME_URL="https://{APP_NAME}.fly.dev"
+  APP_STATIC_URL="https://{APP_NAME}.fly.dev"
+  GRIST_SINGLE_ORG="docs"
+  PORT = "8080"
+  FLY_DEPLOY_EXPIRATION = "{FLY_DEPLOY_EXPIRATION}"
+
+[experimental]
+  allowed_public_ports = []
+  auto_rollback = true
+
+[[services]]
+  http_checks = []
+  internal_port = 8080
+  processes = ["app"]
+  protocol = "tcp"
+  script_checks = []
+  [services.concurrency]
+    hard_limit = 25
+    soft_limit = 20
+    type = "connections"
+
+  [[services.ports]]
+    force_https = true
+    handlers = ["http"]
+    port = 80
+
+  [[services.ports]]
+    handlers = ["tls", "http"]
+    port = 443
+
+  [[services.tcp_checks]]
+    grace_period = "1s"
+    interval = "15s"
+    restart_limit = 0
+    timeout = "2s"
+
+[mounts]
+source="{VOLUME_NAME}"
+destination="/persist"