### Description

The health API response can become a few MBs (2-3MB if 50K indices are affected).

In less extreme situations the response can be in the 10s/100s of KB. 

It might be worthwhile looking into chunking its response (this might provide clients with a better experience too)
server/src/test/java/org/elasticsearch/health/HealthIndicatorResultTests.java
result.toXContent(builder, ToXContent.EMPTY_PARAMS);
        Map<String, Object> xContentMap = XContentHelper.convertToMap(BytesReference.bytes(builder), false, builder.contentType()).v2();
        assertEquals(status.xContentValue(), xContentMap.get("status"));
        assertEquals(symptom, xContentMap.get("symptom"));
        assertEquals(detailsMap, xContentMap.get("details"));
        List<Map<String, Object>> expectedImpacts = new ArrayList<>();
        Map<String, Object> expectedImpact1 = new HashMap<>();
        expectedImpact1.put("id", HEALTH_API_ID_PREFIX + name + ":impact:" + impact1Id);
        expectedImpact1.put("severity", impact1Severity);
        expectedImpact1.put("description", impact1Description);
        expectedImpact1.put("impact_areas", List.of(firstImpactArea.displayValue()));
        Map<String, Object> expectedImpact2 = new HashMap<>();
        expectedImpact2.put("id", HEALTH_API_ID_PREFIX + name + ":impact:" + impact2Id);
        expectedImpact2.put("severity", impact2Severity);
        expectedImpact2.put("description", impact2Description);
        expectedImpact2.put("impact_areas", List.of(secondImpactArea.displayValue()));
        expectedImpacts.add(expectedImpact1);
        expectedImpacts.add(expectedImpact2);
        assertEquals(expectedImpacts, xContentMap.get("impacts"));
        List<Map<String, Object>> expectedDiagnosis = new ArrayList<>();
        {
            Map<String, Object> expectedDiagnosis1 = new HashMap<>();
            expectedDiagnosis1.put("id", HEALTH_API_ID_PREFIX + name + ":diagnosis:" + diagnosis1.definition().id());
            expectedDiagnosis1.put("cause", diagnosis1.definition().cause());
            expectedDiagnosis1.put("action", diagnosis1.definition().action());
            expectedDiagnosis1.put("help_url", diagnosis1.definition().helpURL());
            if (diagnosis1.affectedResources() != null) {
                XContentBuilder diagnosisXContent = XContentFactory.jsonBuilder().prettyPrint();
                diagnosis1.toXContent(diagnosisXContent, ToXContent.EMPTY_PARAMS);
                expectedDiagnosis1.put(