linea-mainnet: disable eth_getProof on pruned geth upstream for rpc-us-40

DRPC gateway probes eth_getProof and marks the upstream 81% unavailable
when the pruned geth node returns 'header not found'. This is a false
positive - the node is healthy and advancing. Disable eth_getProof on the
linea pruned geth upstream to prevent DRPC from marking it unavailable.

Mirrors the existing pattern for BSC minimal in rpc-us-41.yaml.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

main_configs/rpc-us-40.yaml

@@ -0,0 +1,26 @@
+upstreams:
+  - id: us-40-linea-mainnet-geth
+    labels:
+      provider: local
+    connection:
+      generic:
+        rpc:
+          url: http://linea-mainnet-geth:8545
+        ws:
+          frameSize: 20Mb
+          msgSize: 50Mb
+          url: ws://linea-mainnet-geth:8545
+    chain: linea
+    method-groups:
+      enabled:
+        - debug
+        - filter
+    methods:
+      disabled:
+        - name: debug_traceBlockByHash
+        # pruned geth lacks the state to serve eth_getProof; the drpc gateway
+        # probes it and marks the whole upstream unavailable on "header not
+        # found" (especially while catching up after a restart).
+        - name: eth_getProof
+      enabled:
+        - name: txpool_content