Draft: rpc: Deprecate yay RPCs

Context

This is a follow-up of !7960 (merged), which deprecated "Yay" in favor of "Yea" in the documentation. This follow-up also changes the RPCs dealing with ballots as inputs or as output.

The encoding of ballots impacts the inputs or results of type operation.contents and operations.contents_and_result in the following RPCs:

• GET ../<block_id>?[force_metadata]&[metadata=<metadata_rpc_arg>]
• POST ../<block_id>/helpers/preapply/block?[sort]&[timestamp=]
• POST ../<block_id>/helpers/preapply/operations
• GET ../<block_id>/operations?[force_metadata]&[metadata=<metadata_rpc_arg>]
• GET ../<block_id>/operations/<list_offset>?[force_metadata]&[metadata=<metadata_rpc_arg>]
• GET ../<block_id>/operations/<list_offset>/<operation_offset>?[force_metadata]&[metadata=<metadata_rpc_arg>]

It also impacts the current ballot in the result of the following RPCs:

• GET ../<block_id>/context/delegates/
• GET ../<block_id>/context/delegates//voting_info

Todo:

• support the deprecated value "Yea" for some time, if needed
• announce the deprecation strategy
• update the broken tests (unless deprecation support)

Manually testing the MR

Checklist

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