ENH: options for controlling features
Various feature changes in the future might be invasive to the long-term support (LTS) concept. IOW, having a deprecation warning for Panel. So allow an option to control this.
- Deprecate `Panel`, #13563
- Deprecate `.ix`: https://github.com/pydata/pandas/issues/14218

something like:

`options.features.panel = 'warn' | 'raise' | 'ignore'`
`options.features.ix = 'warn' | 'raise' | 'ignore'`

These would default to `warn`, but can then be user settable. Normally don't like changes to global state, but if you _are_ using a 'deprecated' feature, easiest to silence things like this.
