Use normative key words for MeterProvider's Meter API parameters (#3069)

* Use normative key words for Meter API params

Communicate the `name` parameter is an absoluter requirement for the API
to accept as a parameter and the other parameters are truly optional by
using key words adopted by this specification and defined in BCP-14.

specification/metrics/api.md

@@ -121,7 +121,7 @@ The `MeterProvider` MUST provide the following functions:
 
 This API MUST accept the following parameters:
 
-* `name` (required): This name SHOULD uniquely identify the [instrumentation
+* `name`: This name SHOULD uniquely identify the [instrumentation
   scope](../glossary.md#instrumentation-scope), such as the
   [instrumentation library](../glossary.md#instrumentation-library) (e.g.
   `io.opentelemetry.contrib.mongodb`), package,
@@ -140,12 +140,29 @@ This API MUST accept the following parameters:
   implementation which is not even observability-related). A MeterProvider could
   also return a no-op Meter here if application owners configure the SDK to
   suppress telemetry produced by this library.
-* `version` (optional): Specifies the version of the instrumentation scope if the scope
+
+  The `name` needs to be provided by a user. If possible, the API SHOULD be
+  structured so a user is obligated to provide this parameter. If it is not
+  possible to structurally enforce this obligation, the API MUST be documented
+  in a way to communicate to users that this parameter is needed.
+* `version`: Specifies the version of the instrumentation scope if the scope
   has a version (e.g. a library version). Example value: `1.0.0`.
-* [since 1.4.0] `schema_url` (optional): Specifies the Schema URL that should be
-  recorded in the emitted telemetry.
-* [since 1.13.0] `attributes` (optional): Specifies the instrumentation scope attributes
-    to associate with emitted telemetry.
+
+  Users can provide a `version`, but it is up to their discretion. Therefore,
+  this API needs to be structured to accept a `version`, but MUST NOT obligate
+  a user to provide one.
+* [since 1.4.0] `schema_url`: Specifies the Schema URL that should be recorded
+  in the emitted telemetry.
+
+  Users can provide a `schema_url`, but it is up to their discretion.
+  Therefore, this API needs to be structured to accept a `schema_url`, but MUST
+  NOT obligate a user to provide one.
+* [since 1.13.0] `attributes`: Specifies the instrumentation scope attributes
+  to associate with emitted telemetry.
+
+  Users can provide attributes to associate with the instrumentation scope, but
+  it is up to their discretion. Therefore, this API MUST be structured to
+  accept a variable number of attributes, including none.
 
 Meters are identified by `name`, `version`, and `schema_url` fields.  When more
 than one `Meter` of the same `name`, `version`, and `schema_url` is created, it