Enable fine-grained visibility controls for group members

[ericmeadows]

Fixes #415

In order to add somewhat fine-grained display functionality, we have submitted the work we did internally to limit certain monitors from being publicly visible within groups. This allows teams to expand the items in a healthcheck without displaying those results publicly. This is somewhat similar, but more-enhanced, functionality from Kuma Uptime. In order to accomplish this, there needed to be a "two-way" switch that allows for one setting to override the other - members of a group can set their own visibility in a group setting, and the parent can turn off the visibility for all children.

Here's the rough user story/specification:

• An administrator should be able to:
  • See all healthchecks in a group, including their status
  • Quickly determine which healthchecks are going to be publicly hidden
  • Quickly edit the visibility of a groups children from the parent
  • Edit the visibility of a child from all groups when editing the child itself
• A user should be able to:
  • Not see the drilldown button when:
    • There are no children with the show visibility in group setting
    • The parent does not allow children to be visible
  • See a drilldown when there are 1 or more children of a group that are publicly visible and the parent enables drilldown functionality
  • Not see individual pages for children of a group when:
    • There are no children with the show visibility in group turned on
    • The parent does not allow children to be visible
  • See individual pages when:
    • A child has show visibility in group turned on
    • The parent has show visibility of children turned on

Here's the functionality checklist:

• Migration that adds new fields
• Backend calculation for group member drilldown
  • UI button shows/hides appropriately
• Individual Monitor
  • Data propagation for Update/Create functionality
  • Data propagation on Get functionality
  • Checkbox UI
• Group Monitor
  • Data propagation for Update/Create functionality
  • Data propagation on Get functionality
  • Checkbox UI
• Group page
  • Hide individually-hidden monitors when logged-out
  • Show * when logged-in to let users know it's not visible publicly
    • Add internationalization for text
• Return 401 when:
  • Parent disallows group members from being views
  • Child is set to not show inside a group
• Self-review to minimize changes and ensure debugging efforts are stripped.

Possible future functionality (feel free to request this if really needed):

• Show * on the main page when the drill-down is going to be disabled publicly
• Show i18n text that shows what the * means
• Handle a child being shown in multiple groups where 1 parent allows children to be shown and another does not
  • This was skipped in order to get the basic feature shipped (we need this)

[ericmeadows]

@rajnandan1 - can you take a look?

[rajnandan1]

let us tiny int for this, since there are nuances of how boolean is interpreted for pg/mysql/sqilite

[rajnandan1]

can you add some screen shots
admin + page