refactor(dre): implementing background checks for upgrading

[NikolaMilosa]

As it says, this PR moves checking for new releases to a background thread, meaning it doesn't halt the execution of the commands.
Example of running any command when there is a new release available:

./target/debug/dre registry > /dev/null                                                        
 INFO  dre > Running version 0.4.0-2faf0cb-dirty
 INFO  dre::ic_admin > Using ic-admin: /home/nikola/bin/ic-admin.revisions/b39f782ae9e976f6f25c8f1d75b977bd22c81507/ic-admin
 INFO  ic_management_backend::registry > Using local registry path for network mainnet: /home/nikola/.cache/ic-registry-cache/mainnet/local_registry
 INFO  ic_management_backend::git_ic_repo > IC git repo path: /home/nikola/.cache/git/ic, lock file path: /home/nikola/.cache/git/ic.lock
 INFO  dre                                > There is a new version '0.4.1' available. Run 'dre upgrade' to upgrade

Example of running proposed dre upgrade:

./target/debug/dre upgrade                                                             
 INFO  dre > Running version 0.4.0-2faf0cb-dirty
 INFO  dre > Binary not up to date. Updating to 0.4.1
[00:00:00] [========================================] 1.45 KiB/1.45 KiB (0s) Done                                                                                                    
INFO  dre > Asset downloaded successfully
[00:00:04] [========================================] 49.87 MiB/49.87 MiB (0s) Done                                                                                                  
INFO  dre > Upgraded: 0.4.0-2faf0cb-dirty -> 0.4.1

NOTICE:
Since this is a now a subcommand, it is assumed that when you run dre upgrade you want to upgrade, thus the prompting for confirmation has been removed.

[DFINITYManu]

This is very cool! Thank you!

[sasa-tomic]

LGTM, thanks!