Pass some rpc/blockchain RPC results and examples to RPCHelpMan

Summary: Partial backport of Core PR14987

Test Plan:
On master:

ninja
./bitcoind
./bitcoin-cli help > RPCs
./getrpchelps.sh RPCs master

Then on the patched branch:

ninja
./bitcoind
./getrpchelps.sh RPCs patched
./checkrpc.sh RPCs master patched blockchain1.diff

Verify changes in blockchain1.diff.

Scripts:

blockchain1.diff:

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5875