add feature flag for automate-mst-consent

[janechodance]

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Summary

Added the form526_0781_automate_mst_consent feature flag to config/features.yml to control the automatically sending mst consent

Related issue(s)

department-of-veterans-affairs/va.gov-team#137308

Testing done

• New code is covered by unit tests
• Describe what the old behavior was prior to the change
• Describe the steps required to verify your changes are working as expected. Exclusively stating 'Specs run' is NOT acceptable as appropriate testing
• If this work is behind a flipper:
  • Tests need to be written for both the flipper on and flipper off scenarios. Docs.
  • What is the testing plan for rolling out the feature?

Screenshots

Note: Optional

What areas of the site does it impact?

(Describe what parts of the site are impacted andifcode touched other areas)

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

Requested Feedback

(OPTIONAL)What should the reviewers know in addition to the above. Is there anything specific you wish the reviewer to assist with. Do you have any concerns with this PR, why?

[Copilot]

Pull request overview

Adds a new Flipper feature toggle to vets-api to gate automated MST-consent behavior associated with the Form 526 / Form 0781 submission flow.

Changes:

• Added form526_0781_automate_mst_consent feature flag entry in config/features.yml.
• Configured the flag as actor_type: user and enabled it in development by default.

[Copilot]

The description text has grammatical issues and inconsistent capitalization ("mst" vs "MST"), which makes the feature flag intent harder to understand. Consider rephrasing to something like: "Enables MST consent to be sent automatically when Form 0781 is submitted as part of the Form 526 flow, if the veteran has given consent."

Suggested change

	description: Enables mst consent to send automatically when the 0781 form is submitted in the 526 flow, when the veteran given consent
	description: Enables MST consent to be sent automatically when Form 0781 is submitted as part of the Form 526 flow, if the veteran has given consent.