Convert ExternallyManagedKeyHandler to TypeScript

[pushpitkamboj]

converted the file to typescript.
it solves issue #2904

Description

added the required types for the file to typescript.

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[AnvayKharb]

#2904
This pull request migrates the ExternallyManagedKeyHandler module from JavaScript to TypeScript, improving type safety and maintainability. The main changes include the addition of a new KeyInfo interface to define encryption key information and adjustments to the setKey method to use this interface.

TypeScript migration and type improvements:

• Converted ExternallyManagedKeyHandler.js to ExternallyManagedKeyHandler.ts, adding explicit type annotations for the class and its methods. [1] [2]
• Introduced a new KeyInfo interface to clearly define the structure of encryption key information passed to the setKey method.

API adjustments:

• Updated the setKey method to accept a KeyInfo object and adjusted its usage of the encryption key and index to match the new interface.

[naman9271]

@pushpitkamboj @AnvayKharb Welcome to the community, and thanks for your contribution and PR but i have already worked on it and raised a PR #2856
Thank you