[IMP] travis2docker: Preinstall VS Code server and add devcontainer.json

[moylop260]

Reimplements the idea of #169 (credit to @antonag32) on top of the current main, extended with build-time pre-installation of the VS Code tooling. Related to #158.

Everything is opt-in with the environment variable DEPLOYV_VSCODE=1, so vim/terminal users are not affected at all (no extra build time, no extra files):

DEPLOYV_VSCODE=1 travisfile2dockerfile git@github.com:Vauxoo/forecast.git 8.0

When enabled:

• The Dockerfile pre-installs the VS Code server and extensions at build time, so attaching VS Code to the container does not download/install anything live:
  • The server version is pinned to the commit of the local code binary (code --version), falling back to the latest stable when code is not in PATH. If the pinned server ever mismatches the client, VS Code just downloads its own version as usual (graceful fallback).
  • The extensions come from the existing templates/.vscode/extensions.json (single source of truth, no duplicated list) and are installed into ~/.vscode-server/extensions, which is server-version independent, so they survive client upgrades.
  • The download handles both x86_64 and arm64 images.
• A .devcontainer.json is generated next to the Dockerfile pointing to the image built by 10-build.sh (instead of rebuilding from the Dockerfile, which would lose --build-env-args), with remoteUser: odoo, workspaceFolder: /home/odoo/instance and python.analysis.extraPaths for Odoo source navigation. Opening the generated folder in VS Code offers Reopen in Container automatically.

Differences vs #169: rebased onto the pathlib/deployv-only codebase, remoteUser is odoo instead of root, uses image instead of dockerFile, the extension list is not duplicated, gated behind the env var, and covered by tests.

• TODO: Check vscode opening a .py file not found interpreter python error