[v6] Inconsistent story for relative paths with BeforeContainer

[fflaten]

Checklist

• Issue has a meaningful title
• I have searched the existing issues. See all issues
• I have tested using the latest version of Pester. See Installation and update guide.

What is the issue?

With Pester.BeforeContianer.ps1 you get:

• $pwd = Working dir when calling Invoke-Pester. Unstable 👎
• $PSScriptRoot = Folder for Pester.BeforeContainer. Stable 👍

With Run.BeforeContainer you only get the unstable $pwd as there's no file path to calculate $PSScriptRoot from.

Expected Behavior

Provide a consistent path reference/anchor or recommendation

Steps To Reproduce

$c = New-PesterConfiguration
$c.Run.ScriptBlock = { Describe 'd' { It 'i' {} } }
$c.Run.BeforeContainer = { Write-Host "BeforeContainer script. PSScriptRoot: '$PSScriptRoot' . Pwd: '$pwd'" }
invoke-pester -Configuration $c

Describe your environment

No response

Possible Solution?

Maybe expose RepoRoot as a variable which would stable for all containers?

[fflaten]

Side note: Do we need to support BeforeContainer as a configuration option? While nice for debugging, it has some quirks like this.

It would also have limitations with a potential folder-scoped idea like this #2772 (comment) . Though we could workaround that by exposing the current container in some way (#2839) so conditions could be used in BeforeContainer