update(userspace): enhancements in rule description feature

[jasondellaluce]

What type of PR is this?

/kind cleanup

/kind feature

Any specific area of the project related to this PR?

/area engine

What this PR does / why we need it:

Which issue(s) this PR fixes:

This mostly involves Falco -L, and the engine in general, from different fronts:

• Uniform usage of nlohmann::json instead of alternating it with jsoncpp -- we may be on the road for avoid having two json libs in the project
• Avoiding memory copies wherever possible
• The stdout printout is not taken care of by the Falco app and not the engine, for better separation of concerns
• Falco -L now can be used in combination with -V for parity, given that it was already compatible with -r, also enabling the feature of validating a ruleset and showing its internals all in a single step

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

update(userspace): enhancements in rule description feature

[jasondellaluce]

/milestone 0.37.0

[github-actions]

This PR may bring feature or behavior changes in the Falco engine and may require the engine version to be bumped.

Please double check userspace/engine/falco_engine_version.h file. See versioning for FALCO_ENGINE_VERSION.

/hold

[jasondellaluce]

This PR may bring feature or behavior changes in the Falco engine and may require the engine version to be bumped.

This is a false positive IMO, no feature of the language or engine is altered.

/unhold

[incertum]

/approve

[poiana]

LGTM label has been added.

Git tree hash: 18ab6c34944f1c2ee7867428b135b012318afe1e

[incertum]

/approve

[poiana]

LGTM label has been added.

Git tree hash: a8e407571eb4e79214c0f4fdd36e37271b4ec173

[Andreagit97]

/approve

[poiana]

LGTM label has been added.

Git tree hash: cbfce3925c3f5f5ae38e5041b9313783eeead502

[incertum]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Andreagit97, incertum, jasondellaluce

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