meta checks: aggregating multiple checks under a single alias

[shlomi-noach]

This PR introduces meta-checks. From the outside a meta check looks just like any other check. But under the cover a meta check is an aggregation of multiple other checks.

For example, the check api/check/theapp/mysql/cluster1-full can aggregate multiple checks such as api/check/theapp/mysql/cluster1-lag and api/check/theapp/mysql/cluster1-writeload.

Checks can have any name. The above check doesn't have to be named mysql. It can also be named api/check/theapp/foo/bar.

Example configuration:

  "Stores": {
    "Meta": {
        "mysql/cluster1-full": [
            "mysql/cluster1-lag",
            "mysql/cluster1-writeload"
        ]
    },
    "MySQL": {
        ...
    }

cc @github/database-infrastructure @miguelff

[timvaillancourt]

@shlomi-noach 👋 this is a really useful PR, thanks!

Merge conflicts aside, is there anything holding this back? I'm happy to get it mergeable and tested

[shlomi-noach]

@timvaillancourt if I remember correctly, we ended up not needing these changes, and we opted to not merge the PR so as not to introduce unnecessary code and configuration complications. Again if I remember correctly production deployment looked good with no issues.

[shlomi-noach]

Doing personal cleanup of old PRs, this has been stale for 5 years, closing.