Add leadAccountId to ProjectUpdateScheme model

[magalhaes3]

Is your feature request related to a problem? Please describe.
At the moment, there is no way to specify the leadAccountId when updating a project, only when creating the project.
This is required if you're trying to update the lead account for the project using v3 of the Jira API since lead was deprecated, as stated in the update method documentation.

Describe the solution you'd like
I'd like for the ProjectUpdateScheme model to include leadAccountId so we can pass in an account id to update the project lead.

Describe alternatives you've considered
Alternatives would have to use v2 instead of v3.