Fixes #16752 - Extract template code from Host::Managed

Host::Managed contains a lot of code related with determining the
template that a host should have. Other Host objects such as
Host::Discovered might need that logic, without becoming a
Host::Managed....

Fixes #12547 - Added validators to interger fields

With this commit, instead of postgresql exception it will
show proper validation message for interger fields.

fixes #18024 - add 'image' search field to hosts

fixes #17574, #17364 - update scoped_search to 4.x

scoped_search's sort() now accepts a replacement for params which is
filtered in an overridden Foreman sort helper, permitting additional
parameters used in Foreman's index pages.

Replaces :in and :alias in search definitions with preferred keywords.

Fixes #14688 - Power status visible on hosts index page

Fixes #16565 - Correct host search by parameters

Overrides for parameters values caused incorrect results for when
searching by parameter value. This commit fixes those results, and
improves the handling of parameter priorities in general. A new rake
task, `parameters:reset_priorities` is introduced that should be invoked...

Fixes #16491 - Upgrade rubocop to version 0.42

Fixes #16358 - Load dashboard on puppet proxy view

Some changes made to the main dashboard caused the puppet dashboard on
the smart proxy page to break.
This commit also includes small improvements to the dashboard loading
performance.

Fixes #16197 - Host#smart_proxies returns only the host proxies

Doing the following:
- Create 2 smart proxies, one for dhcp/dns/tft/puppetca/puppet, another
for realms. Let's keep the realms proxy off, so it's unreachable.
- Create a hostgroup A that sets domain, subnet, realm, puppet_proxy,...

Fixes #12193 - Stop using counter_cache for host[group] counts

This is aimed to prevent deadlocks caused by Rails' implementation of
counter_cache that is hit when multiple hosts are created or updated at
the same time. An added benefit is that the counters will now display...