[CHORE]: Warn on config values that do not match the schema #8064

Description

Validate config values in setPlotContext against configAttributes and call Lib.warn on a mismatch.

Why should this change be made?

src/plot_api/plot_config.js says valType and values are documentation only, so a bad config value lands in _context in silence and fails somewhere else later.

Full coercion would replace bad values with defaults, which silently changes charts that work today. A warning gives the diagnostic benefit with no behavior change, and the hit rate tells us whether coercion is worth it later.

The metadata supports it: every typed config attribute is self-consistent, with no dflt outside its own values.

Scope

• src/plot_api/plot_api.js - in setPlotContext, run Lib.validate(value, attr) per key and warn on false
• Skip the valType: 'any' attributes. Lib.validate accepts anything for them.