handle enrollments and exposures queries for cirrus

[mikewilli]

• builds enrollment and exposure queries for Cirrus
• adds an enum for the allowed query types
• adds a test to make sure cirrus queries are built properly

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (e5de845) 75.99% compared to head (c2210cf) 76.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #193 +/- ## ========================================== + Coverage 75.99% 76.18% +0.18% ========================================== Files 23 23 Lines 958 974 +16 ========================================== + Hits 728 742 +14 - Misses 230 232 +2 ``` | [Flag](https://app.codecov.io/gh/mozilla/mozanalysis/pull/193/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | Coverage Δ | | |---|---|---| | [py38](https://app.codecov.io/gh/mozilla/mozanalysis/pull/193/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | `76.18% <90.90%> (+0.18%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/mozilla/mozanalysis/pull/193?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | Coverage Δ | | |---|---|---| | [src/mozanalysis/experiment.py](https://app.codecov.io/gh/mozilla/mozanalysis/pull/193?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21vemFuYWx5c2lzL2V4cGVyaW1lbnQucHk=) | `79.09% <90.90%> (+0.58%)` | :arrow_up: |

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