[terraform] create SCM connectors

[jimsheldon]

The terraform subcommand should create SCM and/or Docker connector resource configurations, similar to import/migrate.

Flags such as --github-token or --gitlab-token should result in harness_platform_connector_github or harness_platform_connector_gitlab being written into the configuration, and referenced appropriately in the pipeline yaml.

[jimsheldon]

Changing the title so this is specific to creating examples.

In #76 we are trying to remove SCM calls, so import/migrate will no longer create connectors.

[jimsheldon]

The above is untrue! :)

<provider> import will create the SCM connector if the token is passed, terraform should have the same behavior.