Added a function `enable_rhrepo_and_fetch_repoid` and few fixes.

Added `enable_rhrepo_and_fetch_repoid` function, to group many
steps required for syncing RedHat Repos.

The `sync` function under `Repository` Class now returns a task_id.

Added and Fixed many docstrings.

Updated the import related to cloning manifests.

Added test related to syncing RedHat Repository

Few fixes after Repository.sync returns task_id
```python
repo_id = entities.enable_rhrepo_and_fetchid(
    org_id,
    'product name',
    'reposet name',
    ...
)
```