[Feature] Hot-reload apis.yaml without restarting the gateway (nginx-style reload)

[1-2-3]

Add a way to reload the YAML configuration (apis.yaml and files referenced via include:) while Membrane keeps running, similar to nginx -s reload. Today, any change to routes, targets, plugins, or included fragments appears to require a full process restart (membrane.sh / membrane.cmd), which causes downtime and drops in-flight requests.

Proposed behavior

Reload should:

• Re-read the active configuration source (default conf/apis.yaml, or the path passed via -c)
• Resolve include: recursively (same semantics as startup)
• Validate the new configuration before applying it (schema/parse errors must not take down the running router)
• Apply the new routing/interceptor graph without stopping the JVM
• Emit a clear log line on success or failure (e.g. Configuration reloaded from ... / Reload failed: ...)

Reload should ideally (stretch goals):

• Drain or finish in-flight exchanges on removed/changed listeners where possible
• Leave unchanged endpoints stable (minimal blast radius)
• Support rollback to the last known-good config if apply fails

[rrayst]

Hi @1-2-3 .

There is already #2817 and #2959 .

Feel free to contribute!

Best, Toby