Support reading --privkey-path from process substitution

[doitian]

Expect this command to read privkey from the child process output.

ckb-cli account import --privkey-path <(echo 0x...)

But got this error:

error: Invalid value for '--privkey-path <privkey-path>': path </dev/fd/11> is not file

Related reference about process substitution: https://www.gnu.org/software/bash/manual/html_node/Process-Substitution.html

[github-actions[bot]]

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