fix: rilltime syntax in comparison time range in citation urls

[AdityaHegde]

LLM can use rill time for relative time ranges. Since backend supports it in comparison time range as well, it can use it in comparison as well. But UI doesnt support rill time, leading to removal of comparison all together.

One solution is to resolve the time range during mapping. But since these are relative time ranges the data analysed by llm and the data in the link wont match. The problem with converting to custom is we wont have the watermark history of the metrics view to resolve against.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!