LTR390 separate ALS and UV gain and resolution

[latonita]

Description:

More granular control of gain parameter

Related issue (if applicable): fixes https://github.com/esphome/feature-requests/issues/2765

Pull request in esphome with YAML changes (if applicable): esphome/esphome#7026

Checklist:

• [X] I am merging into next because this is new documentation that has a matching pull-request in esphome as linked above.
  or

• [ ] I am merging into current because this is a fix, change and/or adjustment in the current documentation and is not for a new component or feature.

• [ ] Link added in /index.rst when creating new documents for new components or cookbook.