Update dependency @polkadot/api to v15

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@polkadot/api (source)	^14.3.1 -> ^15.0.1

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Release Notes

polkadot-js/api (@​polkadot/api)

v15.0.1

Compare Source

Breaking Changes:

• Allow external signers to modify the payload (#​6030) (Thanks to https://github.com/Tbaut)
  • Add allowCallDataAlteration to SignatureOptions, and SignerOptions. This will default to true when its not inputted. This is strictly tied to signing payloads via external signers.

Contributed:

• fix(ExtrinsicPayload): decode assetId with and without option (#​6037) (Thanks to https://github.com/carlosala)

Changes:

• Adjust ExtrinsicV5 to fit current spec (#​6029)
  • This removes the signed functionality for ExtrinsicV5 since it is no longer supported
• Update docs for WsProvider, and RpcCore (#​6031)
• Add testing for assetId access from ExtrinsicPayload (#​6033)
• Update Substrate types to 1.16.2 (#​6034)

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