Allow specifying compose version (V1 or V2)

[adamf-datapath]

• Added CompositeBuilder.AssumeComposeVersion(ComposeVersion composeVersion) method.
• Updated the logic in DockerComposeCompositeService.ExtractNames to separate container names with either _ or -, depending on the compose version specified.
• Made DockerComposeCompositeService more extensible by changing the accessibility of some members from private to protected. This allows derived classes to access things such as the config and the hosts/containers collections when overriding methods.

[mariotoffia]

Many thanks for this excellent PR!! @adamf-datapath

Cheers, Mario :)