Add option to specify last release tag name for core subpackages

[MajorLift]

Currently, this tool is set to assume that tag names will be in the @metamask/ namespace, when searching for the last release tag of a subpackage.

With packages that are being migrated into the core monorepo, this is not always the case, especially if they are set to be renamed into the @metamask/ namespace after their migration.

To handle these edge cases, we need to expose an option in the create-release-branch cli that will let us specify the last release tag name for a given subpackage, so that the tool can properly examine the diff between the specified tag and HEAD.

[MajorLift]

This issue can be sidestepped by adding a CHANGELOG entry for the next release version before running create-release-branch.