new(docs): add docs for transform operators and val()

[LucaGuerra]

What type of PR is this?

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

/kind bug

/kind cleanup

/kind design

/kind user-interface

/kind content

/kind translation

/kind event

Any specific area of the project related to this PR?

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

/area documentation

What this PR does / why we need it:

Document new conditions/output operators in Falco 0.38.0

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[Andreagit97]

LGTM

[LucaGuerra]

/hold

until 0.38.0 release

[LucaGuerra]

/assign

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: leogr, LucaGuerra

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Needs approval from an approver in each of these files: - ~~[content/OWNERS](https://github.com/falcosecurity/falco-website/blob/master/content/OWNERS)~~ [LucaGuerra,leogr] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[poiana]

LGTM label has been added.

Git tree hash: 166230aeb3347a0def3e7a8302eb47e7691f9031

[LucaGuerra]

/unhold