feat(526-0781): Create feature flag for automate MST consent

[janechodance]

User Need

When a Veteran submits the 0781 form within the 526EZ flow and has given MST (Military Sexual Trauma) consent, the consent should be sent automatically rather than requiring a manual process.

Description

Add a feature flag form526_0781_automate_mst_consent to config/features.yml in vets-api to control the automatic sending of MST consent when the 0781 form is submitted in the 526 flow. This flag will gate the functionality so it can be incrementally rolled out and rolled back if needed.

Tasks

• Add form526_0781_automate_mst_consent feature flag to config/features.yml
• Implement backend logic gated by the flag (follow-up PR)
• Implement frontend logic gated by the flag (follow-up PR)

Acceptance Criteria

• Feature flag form526_0781_automate_mst_consent exists in config/features.yml
• Flag has actor_type: user and enable_in_development: true
• Flag can be toggled on/off via Flipper

Definition of Done

• Meets acceptance criteria
• Reviewed and approved by product and/or design

Engineering

• All tests pass
• New functionality is covered by unit tests
• Logging and monitoring are implemented (if applicable)

Code Review & Pull Requests

• PR includes Local testing steps
• PR includes Flipper/testing state details (if applicable)
• PR includes Author's local proof of submission screenshot
• Copilot review completed and feedback addressed
• Internal reviewer approved
• Internal reviewer added local proof of submission screenshot
• Code functionality verified on Staging after merge

Refinement Checklist!

• Added description, tasks, and acceptance criteria
• Added estimate
• Labeled with Practice Area (engineer, design, product, data science)
• Labeled with issue type and characteristics of the ticket (bug, accessibility, request, discovery, documentation, research, content, ux testing, front-end, back-end, datadog, etc.)
• Added any other relevant project fields (team, OCTO priority...)
• Added an Epic or Super Epic