Report DOWN on Rest API connection issue in monitor

[xin-hedera]

Description:

This PR changes the cluster health indicator to return DOWN when there is Rest API connection issue.

Related issue(s):

Fixes #8509

Notes for reviewer:

The scenario is, when there is db issue, /api/v1/network/stake will return 500 code at the beginning. However the same db issue will also cause the rest pod readiness probe to fail and eventually mirror-rest service will be unavailable and thus cause connection issue, so we need to report DOWN as well.

Checklist

• [x] Documented (Code comments, README, etc.)
• [x] Tested (unit, integration, etc.)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.41%. Comparing base (1a273a8) to head (726da0e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8585 +/- ## ========================================= Coverage 92.41% 92.41% - Complexity 7474 7475 +1 ========================================= Files 913 913 Lines 29792 29795 +3 Branches 3626 3627 +1 ========================================= + Hits 27531 27534 +3 Misses 1442 1442 Partials 819 819 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud