[Core] Follow industry standards for Golang project folder structure

[Olshansk]

Objective

Follow standard Golang library code practices.

Origin Document

@Gustavobelfort suggested we follow standard project layouts in our V1 repo: https://github.com/golang-standards/project-layout

Goals

• Make the codebase follow best practices in the industry
• Make the codebase easily approachable/navigatable for newcomers

Deliverable

• A PR updating the entire code layout to follow the structure in the guidelines: https://github.com/golang-standards/project-layout

Non-goals / Non-deliverables

• New features
• Business logic modifications

General issue deliverables

• Update the appropriate CHANGELOG
• Update any relevant READMEs (local and/or global)
• Update any relevant global documentation & references

Testing Methodology

• All tests: make test_all
• LocalNet: verify a LocalNet is still functioning correctly by following the instructions at docs/development/README.md

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Creator: @Olshansk
Co-Owners: @Gustavobelfort

[Olshansk]

A first attempt at this was made in #412 but is no longer a priority due to other work. It should still be used as direction for anyone who picks this up in the future. Specifically:

• Mimic the same list of changes as in the previous PR
• Move internal code to an internal directory to be compliant with other go extensions
• Use git mv to track changes easier
• Do not rename app/client to cmd/v1, but potentially just cmd or cli instead