Account impersonation

[marioiordanov]

Usage related changes

Added 4 methods following JSON-RPC spec. Closes #407

Development related changes

Added checks for impersonated accounts in DECLARE and INVOKE handler methods. Added integration tests for account impersonation.

Checklist:

• [ ] Checked the relevant parts of development docs
• [ ] Applied formatting - ./scripts/format.sh
• [ ] No linter errors - ./scripts/clippy_check.sh
• [ ] No unused dependencies - ./scripts/check_unused_deps.sh
• [ ] Performed code self-review
• [ ] Rebased to the latest commit of the target branch (or merged it into my branch)
• [ ] Updated the docs if needed, including the TODO section
• [ ] Linked the issues which this PR resolves
• [ ] Updated the tests if needed; all passing (execution info)