Add per_minute, per_hour, per_day function support

[dai-chen]

Description

This PR extends timechart command's per_* function support (introduced in #4464) by adding three additional per_* functions that normalize metrics to different time units:

• per_minute(field): Calculates the per-minute rate (sum-per-second multiplies by 60)
• per_hour(field): Calculates the per-hour rate (sum-per-second multiplies by 3600)
• per_day(field): Calculates the per-day rate (sum-per-second multiplies by 86400)

TODO: After #4550 is resolved, migrate from the current second-based approach to millisecond-based calculations, e.g., timestampdiff(MILLISECOND, span_start, span_end) to support millisecond span.

Related Issues

Resolves #4350

Check List

• New functionality includes testing.
• New functionality has been documented.
• New functionality has javadoc added.
• New functionality has a user manual doc added.
• New PPL command checklist all confirmed.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff or -s.
• Public documentation issue/PR created.

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[RyanL1997]

Hi @dai-chen , thanks for the change, and it is LGTM. Just left a very minor question on the doc format.