[chore][fluentforwardreceiver] Add stability level per metric (open-telemetry#42960)

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Ex. Adding a feature - Explain what this achieves.-->
#### Description

open-telemetry/opentelemetry-collector#13756
added support for exposing metrics' stability level in the generated
documentation. This PR makes use of this functionality.

We start by setting the stability of all metrics to `development`. More
info about levels can be found at
https://github.com/open-telemetry/opentelemetry-specification/blob/v1.49.0/oteps/0232-maturity-of-otel.md#maturity-levels.

Related to:
- open-telemetry/opentelemetry-collector#11878
- open-telemetry/opentelemetry-collector#13297
-
open-telemetry#35325
-
open-telemetry#42809

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#### Link to tracking issue
Fixes ~

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#### Testing
~

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#### Documentation
Updated

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Signed-off-by: ChrsMark <chrismarkou92@gmail.com>

Author: ChrsMark

receiver/fluentforwardreceiver/documentation.md

@@ -8,40 +8,40 @@ The following telemetry is emitted by this component.
 
 ### otelcol_fluent_closed_connections
 
-Number of connections closed to the fluentforward receiver
+Number of connections closed to the fluentforward receiver [development]
 
-| Unit | Metric Type | Value Type | Monotonic |
-| ---- | ----------- | ---------- | --------- |
-| 1 | Sum | Int | false |
+| Unit | Metric Type | Value Type | Monotonic | Stability |
+| ---- | ----------- | ---------- | --------- | --------- |
+| 1 | Sum | Int | false | development |
 
 ### otelcol_fluent_events_parsed
 
-Number of Fluent events parsed successfully
+Number of Fluent events parsed successfully [development]
 
-| Unit | Metric Type | Value Type | Monotonic |
-| ---- | ----------- | ---------- | --------- |
-| 1 | Sum | Int | false |
+| Unit | Metric Type | Value Type | Monotonic | Stability |
+| ---- | ----------- | ---------- | --------- | --------- |
+| 1 | Sum | Int | false | development |
 
 ### otelcol_fluent_opened_connections
 
-Number of connections opened to the fluentforward receiver
+Number of connections opened to the fluentforward receiver [development]
 
-| Unit | Metric Type | Value Type | Monotonic |
-| ---- | ----------- | ---------- | --------- |
-| 1 | Sum | Int | false |
+| Unit | Metric Type | Value Type | Monotonic | Stability |
+| ---- | ----------- | ---------- | --------- | --------- |
+| 1 | Sum | Int | false | development |
 
 ### otelcol_fluent_parse_failures
 
-Number of times Fluent messages failed to be decoded
+Number of times Fluent messages failed to be decoded [development]
 
-| Unit | Metric Type | Value Type | Monotonic |
-| ---- | ----------- | ---------- | --------- |
-| 1 | Sum | Int | false |
+| Unit | Metric Type | Value Type | Monotonic | Stability |
+| ---- | ----------- | ---------- | --------- | --------- |
+| 1 | Sum | Int | false | development |
 
 ### otelcol_fluent_records_generated
 
-Number of log records generated from Fluent forward input
+Number of log records generated from Fluent forward input [development]
 
-| Unit | Metric Type | Value Type | Monotonic |
-| ---- | ----------- | ---------- | --------- |
-| 1 | Sum | Int | false |
+| Unit | Metric Type | Value Type | Monotonic | Stability |
+| ---- | ----------- | ---------- | --------- | --------- |
+| 1 | Sum | Int | false | development |

receiver/fluentforwardreceiver/internal/metadata/generated_telemetry.go

@@ -16,34 +16,44 @@ telemetry:
     fluent_closed_connections:
       enabled: true
       description: Number of connections closed to the fluentforward receiver
+      stability:
+        level: development
       unit: "1"
       sum:
         value_type: int
         monotonic:
     fluent_events_parsed:
       enabled: true
       description: Number of Fluent events parsed successfully
+      stability:
+        level: development
       unit: "1"
       sum:
         value_type: int
         monotonic:
     fluent_opened_connections:
       enabled: true
       description: Number of connections opened to the fluentforward receiver
+      stability:
+        level: development
       unit: "1"
       sum:
         value_type: int
         monotonic:
     fluent_parse_failures:
       enabled: true
       description: Number of times Fluent messages failed to be decoded
+      stability:
+        level: development
       unit: "1"
       sum:
         value_type: int
         monotonic:
     fluent_records_generated:
       enabled: true
       description: Number of log records generated from Fluent forward input
+      stability:
+        level: development
       unit: "1"
       sum:
         value_type: int