Allow backup of PTR server using backup-postgres

[RMcVelia]

Context

https://trello.com/c/Zkl78tQ5/1977-backup-ptr-database-using-github-action

Update backup-postgres github action so that a PTR postgres server can be backed up

Changes proposed in this pull request

Add ptr-db-server-name to the github action, which will be invoked by konduit -s when specified as an input

Guidance to review

backup of source server (s189d01-rtt-rv-pg) https://github.com/DFE-Digital/register-trainee-teachers/actions/runs/10390616053

backup of PTR copy (s189d01-rtt-rv-pg-ptr) https://github.com/DFE-Digital/register-trainee-teachers/actions/runs/10390757032

Before merge

remove 'for dev testing' commit before merge

Checklist

• [ ] I have performed a self-review of my code, including formatting and typos
• [ ] I have cleaned the commit history
• [ ] I have added the Devops label
• [ ] I have attached the pull request to the trello card

[RMcVelia]

backup ptr database using github action