refs #19589 - ensure that foreman starts in production

this avoids the following error in production (under passenger):
Message from application: uninitialized constant Generators::Base (NameError)
lib/generators/plugin/migration_generator.rb:2:in `<module:Plugin>'...

Fixes #19589 - Added plugin migration generator

Now plugin creators would be able to generate migrations by invoking

``` sh

rails g plugin:migration <migration name and options> --plugin_name=my_plugin

```

Fixes #19700 - update rubocop rules

The following changes have been made:

- Performance/RedundantMerge:
changes lines such as:
```not_found_message.merge! :message => options```
to:
```not_found_message[:message] = options```

- converts str.match() to str =~ ()...

Fixes #19034 - add tasks for clearing expired notifications

Fixes #19295 - use new DHCP API

Fixes #19241 - fix warning: already initialized constant ARGV

Fixes #13772 - orchestration now uses app logger

Fixes #19213 - use provision interface in foreman_url

Before this patch, we were using primary interface for checking on ftfp
proxy and its template feature. Provision interface is more appropriate
for this purposes.

fixes #18445 - always define eager_load_paths, use require_dep

Allows `eager_load!` to be called or enabled in any environment without
loading files under lib/ twice. Switches many `require` calls to Rails'
`require_dependency` to always use its dependency loader, so when eager...

fixes #18719 - replace usage of deprecated Fixnum constant

Most type checks for Fixnum can safely be replaced by Integer, as prior
to Ruby 2.4, Fixnum was a subclass of Integer and so the conditional
holds.