Copybara fails to make GerritApi call with SSO enabled on Gerrit server

On Gerrit side we are moving from Cookie to SSO based authorization. As part of this, all the Gerrit URL's are changing from [https:///r](https:///r) to [https:///r/a](https:///r/a)

After some testing and debugging it was understood that this is not supported as it was giving an error while querying Gerrit using the GerritApi `gerrit_get_changes`

**Copybara logs**
```
INFO: Setting up LogManager
opybara source mover (Version: Unknown version)
Task: Loading config copy.bara.sky
Task: Git Origin: Initializing local repo
WARN: Assuming repository 'https:///r/a/.git' for looking for review 'https:///r/'
Task: Querying Gerrit ('https:///r/a/.git') for active changes with hashtag 'copybara_id_DE0748C6172C03CDF7FDCA09E00A9F7D_'
--------------------------gerrit_get_changes----------------------------r/changes/?q=hashtag%3A%22copybara_id_DE0748C6172C03CDF7FDCA09E00A9F7D_%22+AND+project%3Aa%2F.git+AND+status%3ANEW
WARN: Failed querying the hash tag from gerrit changes. Reason: Error running Gerrit API operation https:///r/changes/?q=hashtag:%22copybara_id_DE0748C6172C03CDF7FDCA09E00A9F7D_%22%20AND%20project:a/.git%20AND%20status:NEW
INFO: Git Destination: skipped push to remote.
```

As a fix, the solution was to make changes to the GerritApi call itself to append the extra /a to the URL but now we have an issue that it fails to authorize

**Error**
```
Task: Querying Gerrit ('https://destination_gerrit_server/r/a/.git') for active changes with hashtag 'copybara_id_DE0748C6172C03CDF7FDCA09E00A9F7D_'
--------------------------gerrit_get_changes----------------------------r/a/changes/?q=hashtag%3A%22copybara_id_DE0748C6172C03CDF7FDCA09E00A9F7D_%22+AND+project%3A.git+AND+status%3ANEW
WARN: Failed querying the hash tag from gerrit changes. Reason: Unauthorized
```

**Code changes**