adding event on triggering rule decoding payload in container

[h4l0gen]

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 is an syscall event which will trigger Decoding payload in container rule
Which issue(s) this PR fixes:

Fixes #115

Special notes for your reviewer:

[h4l0gen]

this rule triggered with use of base64 -d no need to give any encoded payload.
as expected this rule triggered in above terminal when i used base64 -d command inside container. Please provide your feedback @FedeDP

I've used this Dockerfile for creating container

 FROM alpine:latest

RUN apk add --no-cache base64

CMD ["sh"]

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: FedeDP, h4l0gen

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[poiana]

LGTM label has been added.

Git tree hash: ee59191998f4eed3167dd5a8f86695a26310d905