feat: add passwordFile, hashedPasswordFile, githubAuthTokenFile and absProxyBasePath options

[DanielleMaywood]

Closes coder/internal#462

Adds the final four options

• passwordFile
• hashedPasswordFile
• githubAuthTokenFile
• absProxyBasePath

The decision to pass credentials via a file instead of embedding them directly in the devcontainer.json is to allow people the ability to not commit the password to source control.

With these final four options added we should have feature parity with the CLI.

[Copilot]

Pull Request Overview

This PR introduces two new configuration options for code-server to improve security by using external password files instead of hardcoded values.

• Adds the hashedPasswordFile option, which uses an Argon2-hashed password that takes priority over passwordFile.
• Adds the passwordFile option to allow direct password authentication via a file.

Files not reviewed (7)

• src/code-server/devcontainer-feature.json: Language not supported
• src/code-server/install.sh: Language not supported
• test/code-server/code-server-hashed-password-file.sh: Language not supported
• test/code-server/code-server-hashed-password-file/Dockerfile: Language not supported
• test/code-server/code-server-password-file.sh: Language not supported
• test/code-server/code-server-password-file/Dockerfile: Language not supported
• test/code-server/scenarios.json: Language not supported

[mafredri]

Suggested change

	if [[ -f "$PASSWORDFILE" ]]; then
	export PASSWORD="\$(cat '$PASSWORDFILE')"
	export PASSWORD="\$(<"$PASSWORDFILE")"

Minor: useless use of cat 😄 and " is fine within $().

We don't have the same shell safety for inputs here (as with declare -p) but arguably if someone passes a file name with " in it then they might have other problems too.