DOC-5338: RDI enchance observability page with more metrics information

[ZdravkoDonev-redis]

I used some AI magic and a few sources - Example metrics from a running RDI instance, the codebase, Debezium docs, etc.

I think the format is good, but the alerting recommendations I'm not sure if the alerting recommendations are correct.

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-5338-rdi-enchance-obsrevability-page-with-more-metrics-information/integrate/redis-data-integration/observability

[Copilot]

Pull Request Overview

This PR enhances the observability documentation page for RDI by adding detailed metrics tables and alerting recommendations.

• Added a collector metrics table with descriptions and alerting guidelines.
• Introduced a second table covering stream processor metrics with detailed contextual notes.
• Updated the recommended alerting strategy section for critical and informational monitoring.

Comments suppressed due to low confidence (3)

content/integrate/redis-data-integration/observability.md:110

• [nitpick] Consider clarifying which specific states for 'rdi_engine_state' should trigger a critical alert to eliminate ambiguity for users.

| `rdi_engine_state` | Gauge | Current state of the RDI engine with labels for `state` (e.g., STARTED, RUNNING) and `sync_mode` (e.g., SNAPSHOT, STREAMING) | **Critical Alert**: Alert if state indicates failure or error condition |

content/integrate/redis-data-integration/observability.md:106

• [nitpick] Consider expanding the description for 'incoming_records_created' to explain its purpose and usage, since reporting a timestamp as a gauge might be confusing for some users.

| `incoming_records_created` | Gauge | Timestamp when the incoming records counter was created | Informational - no alerting needed |

content/integrate/redis-data-integration/observability.md:55

• [nitpick] Metric naming conventions differ between the first table (CamelCase) and the second table (snake_case). Consider aligning these conventions to avoid potential confusion.

| **ChangesApplied** | Counter | Total number of schema changes applied during recovery and runtime | Informational - monitor for trends |

[andy-stark-redis]

A few minor suggestions and questions, but they're easy to fix, so I'll approve. Great addition to the info in this page :-)