[Enhancement] Generate as many clientId's as how many branches there are when using the qaOnly flag

[SoftVision-CiprianMuresan]

[Notes]:

• With the behavior in An error is displayed when trying to save a new/edited recipe if the ratio fields were focused #517, we have opted to use the qaOnly flag, however, one downside attached to this approach is that only one clientId is visible when viewing the recipe, making the other id hard if not impossible to figure out.
• This is a workflow that QA uses for every experiment and given the behavior in An error is displayed when trying to save a new/edited recipe if the ratio fields were focused #517 we can't control which branch we most likely are enrolled. As such, having as many clientId's as how many branches we set-up in an experiment would help us have more control over the branches we test.
• On the flip side we could create 2 different recipes, each with one of the branches that we have to test, could be considered a workaround. But this would just add more work setting recipes up in the event that experiments have 3+ branches.

[Affected versions]:

• Firefox Nightly 84.0a1, Build ID 20201020094032

[Affected Platforms]:

• Windows 10

[Prerequisites]:

• Have VPN access to the staging environment.
• Have the NDT addon (version 2.1.1) installed on a new profile.

[Steps to reproduce]:

1. Open the Firefox profile from prerequisites and click the NDT button from the Browser Toolbar.
2. Create a new recipe with 2 branches using the qaOnly flag.
3. View the newly created recipe and observe the Bucket Sampling section.

[Expected results]:

• An app.normandy.clientId is displayed for each of the branches that are used in the recipe.

[Actual results]:

• Only one cliendId is displayed.

[mythmon]

This is another thing that is already implemented in the unreleased 2.2 version of NDT (hopefully out next week). It assigns a clientId for each branch, that is guaranteed to enroll in that branch.