feat(poll_scheduler): add cron-based poll scheduling to all connectors

[apachler]

Add cron-based pollSchedule support for all connectors

What

Adds an optional pollSchedule parameter that accepts cron expressions to control poll timing. This enables wall-clock-aligned polling (e.g. exactly at :00, :05, :10) and time-dependent schedules (e.g. faster polling during production, slower on weekends).

Also fixes a missing pollPeriod default in the Modbus Slave connector (config['pollPeriod'] → config.get('pollPeriod', 5000)), which is the only connector that crashes when pollPeriod is omitted.

Configuration

// Simple — clock-aligned every 5 minutes
{ "pollSchedule": "*/5 * * * *" }

// Multiple schedules with labels
{ "pollSchedule": [
    { "cron": "*/1 6-22 * * 1-5", "label": "day-shift" },
    { "cron": "*/15 * * * 0,6",   "label": "weekend" }
  ]
}

// Disabled (default in sample configs)
{ "pollSchedule": null }

pollSchedule takes precedence over pollPeriod when present. A value of null (or omitting the key entirely) keeps the original pollPeriod behavior unchanged.

Note: All sample configs (thingsboard_gateway/config/*.json) now ship with "pollSchedule": null so the option is visible but inactive by default. To enable, replace null with a cron string or an array of schedule objects as shown above.

Changes

• New module: thingsboard_gateway/tb_utility/poll_scheduler.py — PollScheduler, PollScheduleEntry, compute_next_poll()
• New dependency: croniter>=1.3.8 (depends only on python-dateutil, already in the tree)
• Bug fix: connectors/modbus/slave.py — add missing pollPeriod default (5000ms)
• All polling connectors: Modbus, OPC-UA, BACnet, BLE, SNMP, CAN, FTP, ODBC, Request — minimal change: instantiate PollScheduler from config, use compute_next_poll() instead of monotonic() + poll_period

Breaking changes

None.

[samson0v]

Hi @apachler, thanks for your contribution!
Can we plan a review of this feature on the release v.3.8.4?

[apachler]

Hi @samson0v, sure, let me know what you need from me ;)