Add expose_ports config option to publish extra container ports - #433

Motivation

DEVX-994 asks for a way to expose extra container ports (e.g. port 53 for the emulator's DNS server, --host-dns in v1) beyond what lstk publishes by default. Per the ticket's own suggested approach, this adds a generic expose_ports config option rather than a DNS-specific flag.

Changes

• New expose_ports config option to publish additional ports on the emulator container.
• Validation for the new option, with clear errors on conflicting or malformed entries.
• Existing default port publishing is unaffected.
• Docs updated to cover the new option.

For docs

New config knob, no CLI flag. Add a section under the config.toml reference (near volumes/container_name):

• What it's for: publish container ports lstk doesn't expose by default — e.g. the emulator's DNS server on port 53 (replaces v1's --host-dns).
• Where: expose_ports inside a [[containers]] block.
• Syntax: a list of port numbers and/or Docker-style strings.

  [[containers]]
  type = "aws"
  port = "4566"
  expose_ports = [53, "5354:5353/udp"]

  • 53 → publishes port 53 on the host for both TCP and UDP (a bare number covers both, since DNS needs both).
  • "5354:5353/udp" → host:container/protocol — host port 5354 maps to container port 5353, UDP only.
  • "53/tcp" → protocol-only entry, host port defaults to the same number.
• Failure mode worth calling out: if the host port is already taken, lstk start fails outright (unlike some other lstk ports, this one won't silently skip and continue).
• Network exposure note: expose_ports entries bind to the same host address as the emulator's other published ports. With a non-loopback bind address (e.g. 0.0.0.0), a [53] entry makes the emulator's DNS resolver reachable from the local network — consistent with every other published port, but worth being aware of since DNS is the headline use case.
• Not covered: you cannot use expose_ports to change ports lstk already manages (4566, 443, the 4510-4559 range) — those are fixed regardless of what you put here.

Review

Human review advised — new user-facing config surface, and the bare-port-expands-to-tcp+udp behavior is a judgment call worth a second look.

Tests

• Unit tests: config grammar (mixed int/string TOML, all entry forms, dedup, invalid entries) and merge/skip/warn/UDP-preflight/bind-hint behavior in internal/container.
• Integration tests added in test/integration/start_test.go: default-ports-unchanged, expose+remap+protocol edge cases, port-already-taken, and config validation.
• make test, make lint pass.

Closes DEVX-994