Add help text and update specs.

[MSP-10733](https://jira.tor.rapid7.com/browse/MSP-10733)

# Verification

- [ ] `cd spec/dummy; rails c`
- [ ] `Mdm::Service.search_operator_by_name[:info].help` looks correct
- [ ] `Mdm::Service.search_operator_by_name[:name].help` looks correct
- [ ] `Mdm::Service.search_operator_by_name[:proto].help` looks correct
- [ ] `Mdm::Service.search_operator_by_name[:port].help` looks correct
- [ ] `Mdm::Host.search_operator_by_name[:name].help` looks correct
- [ ] `Mdm::Host.search_operator_by_name[:address].help` looks correct
- [ ] `Mdm::Host.search_operator_by_name[:os_name].help` looks correct
- [ ] `Mdm::Host.search_operator_by_name[:os_flavor].help` looks correct
- [ ] `Mdm::Tag.search_operator_by_name[:name].help` looks correct
- [ ] `Mdm::Tag.search_operator_by_name[:desc].help` looks correct


# Post-merge Steps

- [ ] remove the PRERELEASE constant from version.rb
- [ ] run

        $ rm Gemfile.lock
        $ bundle install
        $ rake release


```ruby
it_should_behave_like 'search_with',
                       MetasploitDataModels::Search::Operator::Multitext,
                       name: :os,
                       operator_names: [
                           :os_name,
                           :os_flavor,
                           :os_sp
                       ]
````

You want to add it or should I?