lldb-dap attach configuration keys naming consistency

For most of the launch and attach configurations, the names are small caps style keys.

However, for attach configurations we support:

* `"gdb-remote-port": int`
* `"gdb-remote-host": string`

These two keys are the only two with dashes.

For consistency, it would be nice to migrate these keys to small caps naming instead, e.g. `gdbRemotePort` and `gdbRemoteHost`.

Or, if we're already doing a migration, I wonder if we could use a `connection` field instead and take the value as a `connection://` style URI.

No file or test is named. Start by locating lldb-dap's attach-configuration handling and determine whether the project wants gdbRemotePort/gdbRemoteHost or a connection URI; done means the chosen naming scheme is agreed and consistently supported.

Written by the indexing model from the issue text.