feat(jsonrpc): add support for allow-insecure-unlock (backport #2375)

[mergify]

Allow insecure account unlocking when account-related RPCs are exposed by http

Description

Closes: #1657

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Author Checklist

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• tackled an existing issue or discussed with a team member
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• targeted the correct branch (see PR Targeting)

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• added a relevant changelog entry to the Unreleased section in CHANGELOG.md
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This is an automatic backport of pull request #2375 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 0c5f7db has failed:

On branch mergify/bp/release/v18.0.x/pr-2375
Your branch is up to date with 'origin/release/v18.0.x'.

You are currently cherry-picking commit 0c5f7db6.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   rpc/backend/backend_suite_test.go
	modified:   rpc/backend/node_info.go
	modified:   rpc/backend/sign_tx.go
	modified:   server/config/config.go
	modified:   server/config/toml.go
	modified:   server/flags/flags.go
	modified:   server/start.go
	modified:   tests/nix_tests/configs/default.jsonnet

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[GAtom22]

close in favor of #2587