[6.17.z] Add Export function to ReportTemplate class

[Satellite-QE]

Cherrypick of PR: #1349

Description of changes

Added export function to ReportTemplate class and also accomodate in path.

Upstream API documentation, plugin, or feature links

/apidoc/v2/report_templates.en.html#description-export

Functional demonstration

In [1]: from robottelo.config import settings
In [2]: from robottelo.hosts import Satellite
In [3]: target_sat = Satellite('sat-ip-addr')
In [4]: rt = target_sat.api.ReportTemplate()
In [5]: print('Available methods:', [method for method in dir(rt) if not method.startswith('_')])
In [6]: print('Has export method:', hasattr(rt, 'export'))

Additional Information

Any additional notes for reviewers, comments about the change, TODO lists on WIP PRs, etc.
Dependent PR: SatelliteQE/robottelo#19367