Timestamp instruction, value, and description updated

- Updated the instruction: Now it clearly guides the user to replace the placeholder timestamp value with a valid one.
- Changed the sample epoch timestamps to placeholder, after discussing with the SME.
- Updated the description of the timestamp key for better readability.

Author: sujitnewrelic

src/content/docs/data-apis/ingest-apis/metric-api/report-metrics-metric-api.mdx

@@ -28,7 +28,7 @@ Follow this example to send your first metric data points to New Relic:
 
 1. Get the <InlinePopover type="licenseKey"/> for the account you want to report data to.
 2. Insert the license key into the following JSON, and then send the JSON to our [endpoint](#api-endpoint).
-3. Update the `timestamp` with a valid epoch timestamp.
+3. Update the `timestamp` value from `CURRENT_TIMESTAMP` to a valid epoch timestamp.
    This example creates a single metric data point for a metric named `memory.heap`, but you can create additional attributes or data points by specifying [metric types](/docs/telemetry-data-platform/ingest-manage-data/understand-data/metric-data-type) or adding [optional `common` blocks](#optional-map-attributes).
 
    ```bash
@@ -40,7 +40,7 @@ Follow this example to send your first metric data points to New Relic:
                "name":"memory.heap", 
                "type":"gauge", 
                "value":2.3, 
-               "timestamp":1704431659000, 
+               "timestamp":CURRENT_TIMESTAMP, 
                "attributes":{"host.name":"dev.server.com"} 
            }] 
        }]'
@@ -194,7 +194,7 @@ The JSON payload uses this structure:
             "name": "service.errors.all",
             "type": "count",
             "value": 15,
-            "timestamp": 1707110059000,
+            "timestamp":CURRENT_TIMESTAMP,
             "interval.ms": 10000,
             "attributes": {
               "service.response.statuscode": "400",
@@ -206,7 +206,7 @@ The JSON payload uses this structure:
             "name": "service.memory",
             "type": "gauge",
             "value": 2.7,
-            "timestamp": 1707110059000,
+            "timestamp":CURRENT_TIMESTAMP,
             "attributes": {
               "host.name": "dev.server.com",
               "app.name": "foo"
@@ -269,7 +269,7 @@ Each metric data point map in the `metrics` array uses the following key-value s
       </td>
 
       <td>
-        <DNT>**Required**</DNT>. The metric's start time in [Unix time](https://currentmillis.com/). The default uses UTC time zone. This field also support seconds, microseconds, and nanoseconds. However, the data will be converted to milliseconds for storage and query. Metrics reported with a timestamp older than 48 hours ago or newer than 24 hours from the time they are reported are dropped.
+        <DNT>**Required**</DNT>. The metric's start time in [Unix time](https://currentmillis.com/). The default uses UTC time zone. This field also support seconds, microseconds, and nanoseconds. However, the data will be converted to milliseconds for storage and query. Metrics reported with a timestamp older than 48 hours in the past or more than 24 hours in the future from the time they are reported are dropped.
       </td>
     </tr>
 
@@ -324,7 +324,7 @@ Each metric data point map in the `metrics` array uses the following key-value s
             "name": "cache.misses",
             "type": "count",
             "value": 15,
-            "timestamp": 1709615659000,
+            "timestamp":CURRENT_TIMESTAMP,
             "interval.ms": 10000,
             "attributes": {
               "cache.name": "myCache",
@@ -335,7 +335,7 @@ Each metric data point map in the `metrics` array uses the following key-value s
             "name": "temperature", 
             "type": "gauge", 
             "value": 15, 
-            "timestamp": 1709615659000, 
+            "timestamp":CURRENT_TIMESTAMP, 
             "attributes": { 
               "city": "Portland", 
               "state": "Oregon" 
@@ -351,7 +351,7 @@ Each metric data point map in the `metrics` array uses the following key-value s
               "max": 0.001708826
             },
             "interval.ms": 10000, 
-            "timestamp": 1709615659000,
+            "timestamp":CURRENT_TIMESTAMP,
             "attributes": {
               "host.name": "dev.server.com",
               "app.name": "foo"