fix(pds-multiselect): add csrfHeaderName prop

[QuintonJason]

Description

The component documentation showed a csrfHeaderName prop, but it wasn't actually implemented. The CSRF header was hardcoded to 'X-CSRF-Token' in both async fetch and create operations, preventing users from customizing it for frameworks that use different conventions (e.g., Django uses X-CSRFToken, Express may use X-XSRF-Token).

Solution

• Added csrfHeaderName prop with default value 'X-CSRF-Token'
• Updated fetchOptions() method to use configurable header name
• Updated createOption() method to use configurable header name
• Updated TypeScript definitions for both web component and React usage

Fixes DSS-125

Type of change

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• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

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• unit tests
• e2e tests
• accessibility tests
• tested manually
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Test Configuration:

• Pine versions:
• OS:
• Browsers:
• Screen readers:
• Misc:

Checklist:

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• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Design has QA'ed and approved this PR

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[pixelflips]

Seems fine to me. Maybe run coderabbit just for an extra check.

[pixelflips]

Also some weird labels on the PR, but not sure if that effects anything or not.