Add explicit JSON tags for OptimizelyConfig.

[mikecdavis]

Summary

• Add JSON tags to OptimizelyConfig

Marshaling of the OptimizelyConfig into JSON was picking up the literal struct field names. This change uses JSON tags to map the struct fields to a more JSON friendlier representation.

Before:

"ExperimentsMap": {
    "sample_test": {
        "ID": "10000",
        "Key": "sample_test",
        "VariationsMap": {
            "sample_variation": {
                "FeatureEnabled": true,
                "ID": "20000",
                "Key": "sample_variation",
                "VariablesMap": {
                    "sample_variable": {
                        "ID": "30000",
                        "Key": "sample_variable",
                        "Type": "string",
                        "Value": "winning"
                    },

After:

"experimentsMap": {
    "sample_test": {
        "id": "10000",
        "key": "sample_test",
        "variationsMap": {
            "sample_variation": {
                "featureEnabled": true,
                "id": "20000",
                "key": "sample_variation",
                "variablesMap": {
                    "sample_variable": {
                        "id": "30000",
                        "key": "sample_variable",
                        "type": "string",
                        "value": "winning"
                    },      

[jaeopt]

LGTM

[mikeproeng37]

Lgtm

[pawels-optimizely]

lgtm