Deprecate 'application orchestration' features

We should deprecate the 'application orchestration' features in the puppet language. This means the following should be flagged as deprecated:

• Keywords site, application, consumes, and produces
• Metaparameters export and consume
• Puppet::Parser::EnvironmentCompiler
• Puppet::Parser::Compiler::CatalogValidator::SiteValidator & Puppet::Parser::Compiler::CatalogValidator::EnvironmentRelationshipValidator
• Resource kinds: application, site, capability_mapping
• Puppet::Type#is_capability? and application?
• Environment catalog REST API: https://puppet.com/docs/puppet/latest/http_api/http_environment.html

Deprecation also needs to be marked in documentation and in specifications. The documentation is here: https://puppet.com/docs/pe/2017.3/managing_applications.html. When doing this work, please also add the tickets for documentation and specification deprecations.

The intent is to remove these features in Puppet 7.0.0.

Deprecation is easy as it can be done during validation of the parsed result. Removal is a bit more involved as there is a separate "site catalog compiler" and related features to remove. When spending time on the deprecation it is worth also writing the tickets for the removal.