feat(metrics): Add maximum length for metric components (#1286)

src/docs/sdk/metrics.mdx

@@ -61,12 +61,11 @@ class Aggregator:
 
 ## Normalization
 
-Normalization shall be done for `statsd` envelope items with unicode support if possible.
-
-* **Namespaces and Units:** regex `[^a-zA-Z0-9_]+` with no replacement character.
-* **Metric Keys/Names:** regex `[^a-zA-Z0-9_\-.]+` with replacement character `_`.
-* **Tag Keys:** regex `[^a-zA-Z0-9_\-.\/]+` with no replacement character.
-* **Tag Values:** See below
+Normalization shall be done for `statsd` envelope items with unicode support if possible:
+* **Metric Name**: Regex `[^a-zA-Z0-9_\-.]+` with replacement character `_`.
+* **Metric Namespace and Unit**: Regex `[^a-zA-Z0-9_]+` with no replacement character.
+* **Metric Tag Key**: Regex `[^a-zA-Z0-9_\-.\/]+` with no replacement character.
+* **Metric Tag Value**: See below.
 
 {/* Internal note: We can't use `\w` instead of `a-zA-Z0-9` because on some Regex engines `\w` includes chars such as `ä`, `ö` or `é`. */}
 
@@ -84,6 +83,12 @@ Reserved characters for Tag Values are `\n`, `\r`, `\t`, `\`, `|`, `,`. The repl
 | Pipe (`\|`) | `\u{7c}` |
 | Comma (`,`) | `\u{2c}` |
 
+### Maximum Lengths
+
+The lengths of the following components of the `statsd` envelope items should be limited:
+- **Metric Name**: 150 characters.
+- **Metric Unit**: 15 characters.
+
 ## Units
 
 SDKs should permit any string unit, but some of them are known to the system and