Added

Added --with-current-environment flag to the sdk-manager sdk register command. When used with the command, it triggers west zephyr-export using the west command that is available in the user's current environment rather than using a west command from a specified or associated toolchain environment.
The sdk-manager now allows the download region to be specified using the NRFUTIL_REGION environment variable. The following commands are now equivalent:
```
nrfutil sdk-manager install --region cn v3.0.0
```
```
NRFUTIL_REGION=cn nrfutil sdk-manager install v3.0.0
```
Added the sdk-manager sdk search command to allow for searching for available SDKs separately from the toolchains.