feat(profile-sync-controller): add getCustomerServiceToken method and messenger action

[mathieuartu]

Explanation

References

Related to: https://consensyssoftware.atlassian.net/browse/MUL-1982

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Introduces a new authenticated token exchange path used for customer-service identity; behavior aligns with existing auth helpers but any mishandling of returned tokens could affect support tooling access.

Overview
Adds getCustomerServiceToken on AuthenticationController and the AuthenticationController:getCustomerServiceToken messenger action so clients can obtain a short-lived token for Customer Service tooling.

The flow mirrors other bearer-token helpers: optional entropySourceId (defaults to primary SRP), wallet-unlock checks, and login via getAccessToken when needed. The SDK then POSTs /api/v2/customer-service/token with the OIDC access token in Authorization: Bearer, returning the response access_token.

The same API is exposed on JwtBearerAuth, SRP, and SIWE auth flows. Tests and nock/fixture mocks cover success, errors, rate limits, and locked-wallet cases.

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