[BUG] `start -p <name>` treats an optional (`required: false`) dependency as required

Finding: In a single external report (docker/compose issue #14311), on Docker Compose v5.6.0-24-g4e1cd3f4e (main build 4e1cd3f4e) with Docker Engine 29.1.3 on Docker Desktop linux/aarch64, `docker compose -p <name> start` without -f treats a depends_on entry with required: false as required. The reported failure is: service "init" didn't complete successfully: exit 1. The web service stays exited and the command returns exit code 1 (source: https://github.com/docker/compose/issues/14311). Reported conditions: web depends on init with condition service_completed_successfully and required: false, and init runs `exit 1`. The reporter says that after `up -d` and `stop`, `start` with `-f compose.yaml -p optdep` exits 0, warns the optional dependency did not complete, and runs web. Repeating the stop and then running `start` with only `-p optdep` fails, and `ps -a` shows both init and web exited (same source). Reporter hypothesis, not maintainer-confirmed: with -p and no -f, the project is rebuilt from container labels via projectFromName. The reporter says create.go writes the com.docker.compose.depends_on label as service:condition:restart only (for example init:service_completed_successfully:false), and projectFromName reads it back with required hard-coded to true. The reporter also says down, stop and restart compensate by forcing Required = false in getProjectWithResources, while start does not (same source). No maintainer has confirmed this cause in the supplied material. Workaround, as reported and not verified by KFA: run start with the compose file, `-f compose.yaml -p <name>`, so the optional dependency is read from the file. The reporter also says restart works with -p alone (same source). Fix status: UNKNOWN. The reporter proposes adding required as a fourth label field, defaulting to true when missing for labels from older versions, and offers a PR. The reporter says the plan-engine work in #14296 moves start onto that engine but does not touch this label, so the bug would remain. No fix commit or released fix was supplied. The issue is OPEN with no comments. Limitations: this is an external report on a main build, not a released version. KFA did not reproduce it. Affected release versions are unknown.