Expand lstk CLI reference documentation

[gtsiolis]

Summary

Expands the lstk reference page from a short overview into a complete CLI reference — installation, authentication, configuration, the full command set, and troubleshooting. The page is kept focused on lstk only, with no comparison or links to the soon-to-be-deprecated localstack CLI (per the discussion in #700).

What is added

• Commands: start, stop, restart, status, logs, aws, snapshot (save / load / list / remove), reset, volume (path / clear), login, logout, setup, config (path / profile), update, completion.
• Configuration: config-file search order, default config.toml, field reference, emulator types (AWS / Snowflake / Azure), reusable env profiles, and project-local config.
• Authentication: keyring → env → browser resolution order, login / logout, and the file-based token fallback.
• State management: saving and loading snapshots to a local file or a pod: Cloud Pod, the --merge strategies, and listing/removing snapshots.
• Operational reference: global options, interactive vs non-interactive mode, environment variables (including container-injected), OpenTelemetry tracing, logging, shell completions, FAQ, and troubleshooting.

Notes

• Rebased onto main after the Developer Tools reorg; the page now lives at aws/developer-tools/running-localstack/lstk.
• Command syntax, flags, and behavior were verified against the localstack/lstk source (cmd/*.go).
• Follow-up (separate PR): az (Azure CLI proxy), terraform / tf (Terraform proxy), and setup azure are not yet documented.

Fix PRO-313

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