feat(decl): add test command support

[ekoops]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind documentation

/kind tests

/kind feature

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area commands

/area pkg

/area events

What this PR does / why we need it:
This PR adds the test command, that allows to verify that Falco produces the expected alerts as a response to the executed tests. The command allows to connect to Falco via gRPC, through both Unix an AF_INET/AF_INET6 sockets.
The underlying infrastructure has been modified as follows:

• the process chain must be composed at least by one process besides the root process; if no processes are provided in the process chain by the user, a default one is added to it
• test IDs has been added in order to to enable unique identification of the process chain's leaf process. The test ID is stored in the environment of each process chain's process, except the root process. The root process generates a test ID for each test, in the form <ignorePrefix><testUID>. Each process in the chain but the one before the leaf passes the untouched test ID to the child. The one before the leaf passes the test ID without the <ignorePrefix> to the leaf. In this way, the leaf process is the only one having the test ID equals to <testUID>.

The following components have been added:

• alert retriever - collects alerts from Falco (the only available implementation uses gRPC)
• tester - collects alerts from the alert retriever and generates a report

A report is associated with a test (which in turn is associated to a single rule). It contains information regarding (1) the number of alerts successfully matching the expected outcome of the test, and (2) the generated warnings.
A successful match is determined when Falco produces an alert whose fields are equal to the one provided in the expected outcome.
A warning is associated to a single alert in the context of a rule report. A warning is generated if the alert matches the rule name but doesn't match other expected outcome's fields. In the context of a warning, for each expected outcome's field not matching the alert content, a field warning is generated in the report.
If no successful matches and warning are generated during the alerts inspection time interval for a given test, the test is considered failed.

The warning have been added to take into account possible event drops and consequent <NA> values in Falco alerts.

As last features:

• the process chain executable path field is now optional and, if not provided, is automatically generated by the event-generator
• the expected output is now called expected outcome (to distinguish them from Falco outputs)

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ekoops, FedeDP

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[poiana]

LGTM label has been added.

Git tree hash: 562f3715f80e08b07082e79b1f9fb1d9babd1aa8