Genericize freddyk references in docs examples (#2326)

Replaces personal `freddyk`/`freddydk` account names in AL-Go
documentation examples with a generic `myuser` placeholder.

## Changes
- **Scenarios/GetStarted.md**: example clone URL
`https://github.com/freddyk-temp/app1.git` →
`https://github.com/myuser/app1.git`
- **Scenarios/Contribute.md**:
- `$global:E2EgitHubOwner` description: `(like \`freddydk\` or
\`microsoft\`)` → `(like \`myuser\` or \`microsoft\`)` (kept
`microsoft`)
  - `freddyk/AL-Go-PTE@main` → `myuser/AL-Go-PTE@main`
- `freddydk/AL-Go@main\|Templates/Per Tenant Extension` →
`myuser/AL-Go@main\|Templates/Per Tenant Extension`
  - `freddyk/AL-Go-AppSource@main` → `myuser/AL-Go-AppSource@main`
- `freddydk/AL-Go@main\|Templates/AppSource App` →
`myuser/AL-Go@main\|Templates/AppSource App`

Scoped to these two documentation files. Other `freddydk` references
elsewhere in the repo (workflows, workshop, e2e test data) are
functional or out of scope and were intentionally left untouched.

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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>