Standardize Ax Sweeper parameters and remove the Ax upper bound

[omry]

Summary

Complete the Ax portion of #1890 by normalizing the Ax Sweeper search-space configuration with the other Hydra sweepers.

The plugin currently places its configured search space under hydra.sweeper.ax_config.params, while the standardized sweeper interface uses hydra.sweeper.params and Hydra's override grammar.

Scope

• Add the standardized hydra.sweeper.params search-space configuration.
• Convert the standardized Hydra sweep expressions into the corresponding Ax parameter definitions.
• Define a clear compatibility and deprecation path for the existing hydra.sweeper.ax_config.params configuration.
• Remove the <1.3.0 upper bound on ax-platform while retaining the required minimum version.
• Test the plugin against the latest available Ax release and address actual compatibility problems.
• Add regression coverage for configuration-defined parameters, command-line parameters, and their precedence.
• Update the Ax Sweeper documentation and add an appropriate news fragment.

Non-goals

Do not expand the plugin to expose additional modern Ax capabilities as part of this work. Multi-objective optimization, persistence, configurable generation strategies, hierarchical parameters, and similar features remain under #3177 and should be driven by concrete demand.