docs: Add ingestion troubleshooting topic

[JStickler]

What this PR does / why we need it:

• Adds a new topic, Troubleshooting Ingest
• Adds a new topic, Monitoring and alerting ingest
• Adds recommended production limits to the Configuration Best Practices topic.

Special notes for your reviewer:

AI authored using VSCode + VSCode + Claude Sonnet 4 and Cursor + Claude Sonnet 4.5. Two different drafts were generated, then merged and standardized.

Prompts:

• Acting as an experienced technical writer with knowledge of Loki, write a troubleshooting guide for ingesting logs into Loki. Using error messages in the code base and defaults listed in the configuration documentation, document Loki’s error messages, the causes, and what users should do when encountering errors ingesting logs and writing logs to storage.
• Revise and replace Promtail configuration with Alloy configuration.
• Using the following structure: Error message, Cause, Default configuration, Resolution, Properties, fill in any missing details in troubleshooting-ingest.md.
• Add context to the section "Monitoring and alerting". What is the file name where users should include this code example?

This topic is for OSS Loki, but I'd love to reuse it for Cloud Logs. I could use some help flagging which errors would require contacting Grafana Support. And also if any of the errors are "self-healing" in Cloud due to autoscaling, etc.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

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💻 Deploy preview available (docs: Add ingestion troubleshooting topic):

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