Allow using wildcard (*) to search across all columns

Example:
```
| where * contains "hello"
```
Include a warning in a docs, as it against [best practices](https://docs.microsoft.com/en-us/azure/data-explorer/kusto/query/best-practices)

Start at the query-builder entry point for the `where` expression and inspect how `*` and `contains` are represented. The work is done when `| where * contains "hello"` produces a valid query and the documentation warns that this use conflicts with the linked best practices.

Written by the indexing model from the issue text.