Add otlp_exporter_endpoint option to proxy/server as well (#4829)

## Motivation

Currently, only the client supports the `--otlp-exporter-endpoint` flag
and `LINERA_OTLP_EXPORTER_ENDPOINT` environment variable for
OpenTelemetry configuration. The proxy and server binaries always
default to checking the environment variable but don't expose the
command-line option, which is inconsistent with the client.

## Proposal

This PR adds the `otlp_exporter_endpoint` option to both proxy and
server for consistency:

- **Proxy** (`linera-service/src/proxy/main.rs`):
- Added `otlp_exporter_endpoint: Option<String>` field to `ProxyOptions`
- Updated `init_with_opentelemetry` call to pass the endpoint instead of
`None`

- **Server** (`linera-service/src/server.rs`):
- Added `otlp_exporter_endpoint: Option<String>` field to
`ServerCommand::Run` variant
- Created helper function `otlp_exporter_endpoint_for()` to extract
endpoint from command
  - Updated `init_with_opentelemetry` call to use the helper function
- Boxed `CommonStorageOptions` in `ServerCommand::Run` to fix clippy
`large_enum_variant` warning (the `Run` variant became too large after
adding the new field)

Both binaries now consistently accept `--otlp-exporter-endpoint` flag
and `LINERA_OTLP_EXPORTER_ENDPOINT` environment variable, matching the
client's behavior.

## Test Plan

- Verified clippy passes with all features
- Verified clippy passes with no default features
- Confirmed both binaries compile successfully

## Release Plan

- Nothing to do / These changes follow the usual release cycle.

Author: ndr-ds

linera-service/src/proxy/main.rs

@@ -96,6 +96,10 @@ pub struct ProxyOptions {
     /// Runs a specific proxy instance.
     #[arg(long)]
     id: Option<usize>,
+
+    /// OpenTelemetry OTLP exporter endpoint (requires opentelemetry feature).
+    #[arg(long, env = "LINERA_OTLP_EXPORTER_ENDPOINT")]
+    otlp_exporter_endpoint: Option<String>,
 }
 
 /// A Linera Proxy, either gRPC or over 'Simple Transport', meaning TCP or UDP.
@@ -486,7 +490,7 @@ impl ProxyOptions {
         let public_key = &server_config.validator.public_key;
         linera_base::tracing::init_with_opentelemetry(
             &format!("validator-{public_key}-proxy"),
-            None,
+            self.otlp_exporter_endpoint.as_deref(),
         );
 
         let store_config = self

linera-service/src/server.rs

@@ -354,7 +354,7 @@ enum ServerCommand {
 
         /// Common storage options.
         #[command(flatten)]
-        common_storage_options: CommonStorageOptions,
+        common_storage_options: Box<CommonStorageOptions>,
 
         /// Configuration for cross-chain requests
         #[command(flatten)]
@@ -393,6 +393,10 @@ enum ServerCommand {
             env = "LINERA_SERVER_CHAIN_INFO_MAX_RECEIVED_LOG_ENTRIES",
         )]
         chain_info_max_received_log_entries: usize,
+
+        /// OpenTelemetry OTLP exporter endpoint (requires opentelemetry feature).
+        #[arg(long, env = "LINERA_OTLP_EXPORTER_ENDPOINT")]
+        otlp_exporter_endpoint: Option<String>,
     },
 
     /// Act as a trusted third-party and generate all server configurations
@@ -469,6 +473,16 @@ fn main() {
 }
 
 /// Returns the log file name to use based on the [`ServerCommand`] that will run.
+fn otlp_exporter_endpoint_for(command: &ServerCommand) -> Option<&str> {
+    match command {
+        ServerCommand::Run {
+            otlp_exporter_endpoint,
+            ..
+        } => otlp_exporter_endpoint.as_deref(),
+        ServerCommand::Generate { .. } | ServerCommand::EditShards { .. } => None,
+    }
+}
+
 fn log_file_name_for(command: &ServerCommand) -> Cow<'static, str> {
     match command {
         ServerCommand::Run {
@@ -492,7 +506,10 @@ fn log_file_name_for(command: &ServerCommand) -> Cow<'static, str> {
 }
 
 async fn run(options: ServerOptions) {
-    linera_base::tracing::init_with_opentelemetry(&log_file_name_for(&options.command), None);
+    linera_base::tracing::init_with_opentelemetry(
+        &log_file_name_for(&options.command),
+        otlp_exporter_endpoint_for(&options.command),
+    );
 
     match options.command {
         ServerCommand::Run {
@@ -506,6 +523,7 @@ async fn run(options: ServerOptions) {
             wasm_runtime,
             chain_worker_ttl,
             chain_info_max_received_log_entries,
+            otlp_exporter_endpoint: _,
         } => {
             linera_version::VERSION_INFO.log();