Add Support for Managing Service Level Objectives

[platinummonkey]

Adds support for Service Level Objectives /v1/slo endpoints.

Note: This does not include the status API currently, that is a work in flight and will come with a separate PR.

Also updates some packages from datadog_test to datadog. I'm not sure why these were different in the first place

[bkabrda]

Overall this looks really good, but I left some comments that need to be addressed inline.

The test files were in a different package to make sure they do black-box testing (e.g. that none of the internal structures are necessary when actually using the library). I guess I'd prefer keeping things as they are, as this is also completely unrelated to adding SLOs and mixes 2 different features in a single commit.

[platinummonkey]

Context for schemas at the simplest validation level (jsonschema):

Create Schema:

{
        "type": "object",
        "properties": {
            "type": {"type": "string", "enum": ["metric", "monitor"]},
            "name": {"type": "string", "minLength": 1, "maxLength": 16384},
            "monitor_ids": {
                "type": "array",
                "maxItems": 100,
                "uniqueItems": true,
                "items": {"type": "number", "exclusiveMinimum": 0},
            },
            "monitor_search": {"type": "string", "minLength": 1, "maxLength": 16384},
            "query": {
                "type": "object",
                "properties": {
                    "numerator": {"type": "string", "minLength": 1, "maxLength": 65536},
                    "denominator": {"type": "string", "minLength": 1, "maxLength": 65536},
                },
            },
            "tags": {
                "type": "array",
                "maxItems": 128,
                "uniqueItems": true,
                "items": {"type": "string", "minLength": 1, "maxLength": 256},
            },
            "thresholds": {
                "type": "object",
                "patternProperties": {
                    "^[0-9]+[a-z]+$": {
                        "type": "object",
                        "properties": {
                            "slo": {"type": "number", "minimum": 0, "maximum": 100},
                            "warning": {"type": "number", "minimum": 0, "maximum": 100},
                        },
                        "required": ["slo"],
                    }
                },
            },
        },
        "required": ["type", "name", "thresholds"],
    }

Update Schema:

{
        "type": "object",
        "properties": {
            "type": {"type": "string", "enum": ["metric", "monitor"]},
            "name": {"type": "string", "minLength": 1, "maxLength": 16384},
            "monitor_ids": {
                "type": "array",
                "maxItems": 100,
                "uniqueItems": true,
                "items": {"type": "number", "exclusiveMinimum": 0},
            },
            "monitor_search": {"type": "string", "minLength": 1, "maxLength": 16384},
            "query": {
                "type": "object",
                "properties": {
                    "numerator": {"type": "string", "minLength": 1, "maxLength": 65536},
                    "denominator": {"type": "string", "minLength": 1, "maxLength": 65536},
                },
            },
            "tags": {
                "type": "array",
                "maxItems": 128,
                "uniqueItems": true,
                "items": {"type": "string", "minLength": 1, "maxLength": 256},
            },
            "thresholds": {
                "type": "object",
                "patternProperties": {
                    "^[0-9]+[a-z]+$": {
                        "type": "object",
                        "properties": {
                            "slo": {"type": "number", "minimum": 0, "maximum": 100},
                            "warning": {"type": "number", "minimum": 0, "maximum": 100},
                        },
                        "required": ["slo"],
                    }
                },
            },
        },
        "required": ["type"],
    }

ids_schema:

{
        "type": "array",
        "minItems": 1,
        "maxItems": 1000,
        "uniqueItems": true,
        "items": {"type": "string", "minLength": 32, "maxLength": 32},
    }

[bkabrda]

LGTM now, thanks for your work!