Fix/require validator name

[nol4lej]

Require a node name for every node that reports to telemetry

• Validator (testnet, mainnet): VALIDATOR_NAME ships empty and required; compose no longer falls back to Orbinum-Validator. The template's Choose-Your-Validator-Name was the telemetry name of six different operators.
• RPC (testnet, mainnet) and indexer-rpc (testnet): same for RPC_NAME; no fallback to Orbinum-RPC / Orbinum-Indexer-RPC, and the templates no longer ship a name another node already uses.
• docs/rpc-node.md: RPC_NAME marked required.

The relayer (tesseract) does not report to telemetry and is unchanged. Existing deployments keep their .env and are unaffected.

Checked with docker compose config for all five: a missing or empty name fails with the message; a set name renders --name <name>.