Add an optional parameter for Bicep CLI commands to specify the config file to use

**Is your feature request related to a problem? Please describe.**
Currently, users cannot choose which bicep file to use when running `bicep build`.

**Describe the solution you'd like**
Add a parameter to specify a bicep config file path.
```
bicep build ./main.bicep --config ./bicepconfig.prod.json
```

Start by locating the implementation of the `bicep build` command and its current config-file resolution. Trace how the command chooses a config, then verify that the example can select `./bicepconfig.prod.json` without changing default behavior.

Written by the indexing model from the issue text.