[Docs/Tooling] Default to os keyring backend

[okdas]

Objective

We've been using test as a keyring backend as this is the easiest backend for development purposes.
Now that we recommend users to utilize poktrolld binary in different ways, we should default to better security practices.

Origin Document

Goals

• Use os as the default keyring backend per cosmos-sdk recommendations
• Increase end-user security

Deliverables

• Update CLI arguments to default to os keyring backend
• Update documentation/cheat-sheets where users interact with the poktrolld binary to remove the --keyring-backend argument (so it defaults to os)/

Non-goals / Non-deliverables

• Do not remove --keyring-backend=test from the infrastructure. Infrastructure keyring considerations are different from user machines. Node operators should be familiar with their options for keyring backends.

General deliverables

• Comments: Add/update TODOs and comments alongside the source code so it is easier to follow.
• Testing: Add new tests (unit and/or E2E) to the test suite.
• Makefile: Add new targets to the Makefile to make the new functionality easier to use.
• Documentation: Update architectural or development READMEs; use mermaid diagrams where appropriate.

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Creator: @okdas
Co-Owners: TBD

[okdas]

@Olshansk this seems like a good first / community issue

[Olshansk]

@okdas Thanks for creating this. Let's keep it on the backlog and prioritize it when/if we get lots of people complaining about the CLI.