chore(ulmo): backport fixes for verifiable credentials compatibility

[GlugovGrGlib]

Description

Backport of fixes for #2956

• Update Base64 encoding to the URL-safe format that is supported by the latest versions of the LC wallet.
• Update OBV3 achievement id format to be urn compatible.
• Update the didkit package to the openedx fork with the updated DIDKit Core Rust library.

[openedx-webhooks]

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[GlugovGrGlib]

@farhaanbukhsh as there should be an Ulmo.3 release soon according to the release schedule, tagging you for the visibility.

[farhaanbukhsh]

@GlugovGrGlib Noted