Release v0.4.4

Breaking Changes:
[launcher/cmd] Refactor verifier for issue google#419
* Unexport `cmd.Instance`, `cmd.MetadataServer`,
  `cmd.NewMetadataServer`.
* Move package `verifier` from launcher to go-tpm-tools.
  * `verifier.Client`, `verifier.Challenge`, etc.
* Move package `fake` from launcher to go-tpm-tools.
  * `fake.Claims`, `fake.NewClient`, etc.
* Move package `rest` from launcher to go-tpm-tools.
  * `rest.NewClient`, `rest.BadRegionError`, etc.

New Features:
[cmd] Add new command token in the CLI tool google#375
[cmd] add records to cloud logging when fetching token from attestation verifier google#417

Bug Fixes:
Statically link binaries built by goreleaser google#425

Other Changes:
Update readme to gotpm CLi instructions. google#424, google#426

New Contributors:
@Ruide in google#375
@qinkunbao in google#424