CLI instance is now created and initialized lazily

[silvanocerza]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

• What kind of change does this PR introduce?

Enhances the handling of the internal instance used by the cli package.

• What is the current behavior?

The functions that create and initialize the internal instance used in the cli package never check if an instance has been already created nor initialized.

Subsequent calls of instance.Create would create multiple instances, calling instance.Init would reinitialized the specified instance even if already initialized.

• What is the new behavior?

The functions that create and initialize the internal instance used in the cli package now check if an instance has been already created nor initialized.

Calling of instance.Create will create a new instance and cache it, suqsequent calls will return the same instance.
Calling instance.Init won't reinitialized the specified instance if already initialized.

• Does this PR introduce a breaking change, and is
  titled accordingly?

Nope.

• Other information:

Closes #1453.

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[silvanocerza]

Closing this as it will superseded by a future more featureful PR.