fix(metricprovider): fix handling null values in datadog

[y-rabie]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
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When Datadog returns a values list with JSON null value, instead of an empty slice, it gets unmarshalled to a float64 value of 0, which is not what should happen (should be treated as if an empty slice). This is because values is a []float64. Switching it to []*float64 fixes this issue.

I've encountered this issue when doing zero/zero division. For example in a/(a+b), where a and b are both zeros, the a/(a+b) formula returns null. I'm sure this could happen in other cases but I'm not aware of them.

For reference, this is what the datadog response would look like:

{
    "data": {
        "attributes": {
            "columns": [
                {
                    "meta": {
                        "unit": null
                    },
                    "name": "a/(a+b)",
                    "type": "number",
                    "values": [
                        null
                    ]
                }
            ]
        },
        "type": "scalar_response"
    }
}

For the numerator and denominator

                {
                    "meta": {
                        "unit": null
                    },
                    "name": "a",
                    "type": "number",
                    "values": [
                        0.0
                    ]
                },
                {
                    "meta": {
                        "unit": null
                    },
                    "name": "b",
                    "type": "number",
                    "values": [
                        0.0
                    ]
                },
                {
                    "meta": {
                        "unit": null
                    },
                    "name": "a+b",
                    "type": "number",
                    "values": [
                        0.0
                    ]
                },

I've built and tested the image. No need for additional unit tests.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.90%. Comparing base (b0d74e5) to head (f1dfbc7).
Report is 72 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3893      +/-   ##
==========================================
+ Coverage   83.87%   83.90%   +0.03%     
==========================================
  Files         163      163              
  Lines       18564    18564              
==========================================
+ Hits        15571    15577       +6     
+ Misses       2120     2117       -3     
+ Partials      873      870       -3     

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[github-actions]

Published E2E Test Results

  4 files    4 suites   3h 15m 54s ⏱️
113 tests 103 ✅  7 💤 3 ❌
458 runs  425 ✅ 28 💤 5 ❌

For more details on these failures, see this check.

Results for commit f1dfbc7.

[github-actions]

Published Unit Test Results

2 275 tests   2 275 ✅  2m 59s ⏱️
  128 suites      0 💤
    1 files        0 ❌

Results for commit f1dfbc7.