new(docs): dedicated rules contributing guide -> rules maturity definitions and rules acceptance criteria

[incertum]

What type of PR is this?

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

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

Any specific area of the project related to this PR?

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

/area rules

/area registry

/area build

/area documentation

What this PR does / why we need it:

Addressing

• Rules Maturity Definitions -> rules repo
• CONTRIBUTING -> enforce style guide and maturity framework, rules repo

from https://github.com/falcosecurity/falco-website/issues/1009

@LucaGuerra please take it away and directly push to this branch. We could also update the PR template with the new links and checklist in this PR or open a new PR afterwards.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[poiana]

LGTM label has been added.

Git tree hash: b98c78493508e343aa630d8acc2367cbff9de5de

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

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