Add SSH user parameter (#1685)

* Add a configurable SSH user

* Update docs with param

* Indentation of readme

* formatting woes

* Update src/url-helper.ts

Co-authored-by: Josh Gross <joshmgross@github.com>

* Update action.yml

Co-authored-by: Josh Gross <joshmgross@github.com>

* Update genfiles

---------

Co-authored-by: Josh Gross <joshmgross@github.com>

__test__/git-auth-helper.test.ts

@@ -821,6 +821,7 @@ async function setup(testName: string): Promise<void> {
     sshKey: sshPath ? 'some ssh private key' : '',
     sshKnownHosts: '',
     sshStrict: true,
+    sshUser: '',
     workflowOrganizationId: 123456,
     setSafeDirectory: true,
     githubServerUrl: githubServerUrl