Allow "Runner version management" to be disabled

What does this MR do and why?

This merge request allows an instance admin to disable the instance from automatically keeping runners up to date with official runner release versions.

#377371 (comment 1294228003)

Screenshots or screen recordings

New setting in /admin/application_settings/ci_cd#js-runner-settings:

Different behaviour of /admin/runners:

/admin/runners with setting checked (default)	/admin/runners with setting unchecked

How to set up and validate locally

1. Visit /admin/runners and note that Upgrade available and Upgrade recommended sections display.
2. Visit /admin/application_settings/ci_cd#js-runner-settings and uncheck Automatically keep runners up to date with official runner release versions.
3. Visit /admin/runners and note that the two sections now do not display.

GraphQL, run this query in your local /-/graphql-explorer:

query {
  runners {
    nodes {
      upgradeStatus
    }
  }
}

With the setting enabled you should get upgradeStatus values, and with it disabled, you should get null values.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #377371 (closed)