[Docs] Update Penalties by Offense - Slash (%)

[florentina57]

Page URL

https://docs.polkadot.com/infrastructure/staking-mechanics/offenses-and-slashes/#best-practices-to-avoid-slashing

What’s the issue?

Table of penalties by offense in the documentation(see image below) does not reflect the new offenses' names and corresponding slashing percentages for ForInvalidBacked, ForInvalidApproved and AgainstValid per the most recent runtime upgrade 1.6.1, pull request 6827 which states:

ForInvalidBacked (100%) -> hard punishment as backers bear all the responsbility for validity
ForInvalidApproved (2%) -> minor punishment to deter lazy validators
AgainstValid (0%) -> very minor punishment (this causes disablement so opp cost)

Suggested improvement

Replace current table in docs(Stage 3) to table from stage 4(see below) on [Meta] State of Disabling #4359 and adjust to match code:

BackingInvalid -> ForInvalidBacked
ForInvalid vote -> ForInvalidApproved
AgainstValid vote -> AgainstValid