Proposal: SSHDConfig Set Support for Repeatable Keywords

[tgauth]

Summary of the new feature / enhancement

The Microsoft.OpenSSH/SSHDConfig resource currently supports setting sshd_config keywords only when _purge: true, which replaces the entire configuration file. When _purge: false, there is ambiguity in handling keywords that can have multiple arguments. Keywords that can have multiple arguments are further divided into three categories: repeatable, comma-separated, and space-separated. Repeatable keywords (like Subsystem and Port) are spread over multiple lines. Comma-separated (like Ciphers) and space-separated (like AuthorizedKeysFile) keywords can have multiple arguments on a single line. Note, the keywords that are both space-separated and repeatable (i.e. AllowUsers) are classified under "repeatable" for the scope of this discussion.

Proposed technical implementation details (optional)

This proposal builds on the ideas previously discussed in #790 and #1070 to suggest handling these keywords through the following:

1. For all keywords: the Microsoft.OpenSSH/SSHDConfig resource simply passes the declared value through directly (overwriting any existing value(s) that may exist for that keyword)
2. For repeatable keywords: the Microsoft.OpenSSH/SSHDConfig.Repeatable resource with _exist facilitates addition/removal of specific entries

Examples:

Set - behaves as overwrite for all keyword types

- type: Microsoft.OpenSSH/SSHDConfig
  properties:
    PasswordAuthentication: false
    Ciphers:
     - +aes256-gcm@openssh.com
    Port:
     - 2222

Set - behaves as "add" for repeatable keywords

- type: Microsoft.OpenSSH/SSHDConfig.Repeatable
  properties:
    _exist: true
    subsystem:
      - "powershell /usr/bin/pwsh -sshs -NoLogo"
    port:
      - 3333

Set - behaves as "remove" for repeatable keywords

- type: Microsoft.OpenSSH/SSHDConfig.Repeatable
  properties:
    _exist: false
    subsystem:
      - "powershell /usr/bin/pwsh -sshs -NoLogo"
    port:
      - 3333