Add assignment load limit

[crayolakat]

Description

There are time and bandwidth limitations on API calls and their responses when Spoke is deployed on AWS Lambda. This can cause an indefinite 504 error on the TexterTodo page If a texter is assigned a lot of contacts (~>=50,000).

This PR adds an ASSIGNMENT_LOAD_LIMIT variable to limit the number of contacts fetched by the getContacts(...) API call at one time.

Checklist:

• I have manually tested my changes on desktop and mobile
• The test suite passes locally with my changes
• If my change is a UI change, I have attached a screenshot to the description section of this pull request
• My change is 300 lines of code or less, or has a documented reason in the description why it’s longer
• I have made any necessary changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• My PR is labeled [WIP] if it is in progress

[ibrand]

We did a talking PR for this, and agreed that Kathy could add a test to the PR. I'll approve once the test is in!

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[crayolakat]

@ibrand Added Jest tests to verify SQL queries when ASSIGNMENT_LOAD_LIMIT is set and not set. Added ASSIGMENT_LOAD_LIMIT=1 to dev-tools/.env.test to demonstrate in Cypress end-to-end campaign test that all assignments are contacted even if ASSIGNMENT_LOAD_LIMIT is less than the # of assignments a texter has (texter has 2 assignments in the Cypress test).