[CST] Create new feature toggles for LH migration

[jerekshoe]

Background

Currently there is a single feature toggle used for the CST LH migration. This feature toggle determines whether we use the LH Benefits Claims API or the EVSS equivalent when making requests related to claims. Because of a few different situations that have come up, it makes sense for us to split the feature toggle so that can manage our release in a more fine-grained manner. We will be splitting these based on the specific endpoints that are being called with 3 different feature toggles:

• cst_use_lighthouse_index
• cst_use_lighthouse_show
• cst_use_lighthouse_5103

Context

Scenarios that led to this decision: 1) Timeouts on the show endpoint are causing us to delay the entire rollout and we are currently stuck at 5% while waiting for LH to switch their documents provider from EVSS to the LH Benefits Documents API. The index route doesn't have these same issues and other teams have started directing more traffic towards that endpoint (AuthExp is at 50% currently because they only use index) 2) 5103 - There have been multiple issues with the LH implementation of the 5103 endpoint and because of this we have had to switch to using EVSS twice so far. We have had to update the code each time to comment out the LH code and replace it with the existing EVSS code; using a feature toggle instead would make this much easier

Tasks

• [x] Create new feature toggles in vets-api
• [x] Update FE code to use specific feature toggles for individual endpoints
• [ ] Make follow up ticket to remove old feature toggle from vets-api code

Acceptance Criteria

• [x] Each of the 3 endpoint from the LH Benefits Claims API that we utilize in CST are controlled by separate feature toggles

[jerekshoe]

Progress:

• PRs for both of these are in draft now.
• I tested these locally and things seem to work as expected
  • FE tests may need to be updated, will deal with that if need be
• I left the existing feature toggle (cst_use_lighthouse) in place in the BE code because I can't guarantee that the FE/BE deploys will happen at the same time and I don't want to risk there being backlash if the feature toggle disappears. Need to create a follow up ticket to remove the existing feature toggle once we are confident that things are working as expected
• Should test this in staging as well as soon as it deploys to make sure that things are working as expected 1 more time