add loadbalancer rake task

[kayiwa]

add two tasks:
one that allow us to remove an endpoint from serving to the
loadbalancer
another that will put it back on the loadbalancer

closes #218

[coveralls]

coverage: 100.0%. remained the same
when pulling 67bd739 on i218_loadbalancer_rake
into acb1913 on main.

[carolyncole]

Thank you @kayiwa. I think you will need to do a bundle update --conservative health-monitor-rails for this code to work.

[maxkadel]

There's actually a breaking change for Rails 7.2 in the 12.4.1 release, so you have to pin to release 12.4.0. You need to change the line in Gemfile for health-monitor-rails to gem 'health-monitor-rails', '12.4.0'

[maxkadel]

Thanks Francis! Couple small changes.