feat: avm/res/db-for-postgre-sql/flexible-server Add PEs in public …

…mode (#2613)

## Description

<!--
>Thank you for your contribution !
> Please include a summary of the change and which issue is fixed.
> Please also include the context.
> List any dependencies that are required for this change.
-->
Adding possibility to deploy private endpoints when the server is in
public mode.
Closes
[#2578](#2578)

## Pipeline Reference

<!-- Insert your Pipeline Status Badge below -->

| Pipeline |
| -------- |
|
[![avm.res.db-for-postgre-sql.flexible-server](https://github.com/donheerschap/bicep-registry-modules/actions/workflows/avm.res.db-for-postgre-sql.flexible-server.yml/badge.svg?branch=psqlPrivateEndpoint)](https://github.com/donheerschap/bicep-registry-modules/actions/workflows/avm.res.db-for-postgre-sql.flexible-server.yml)
|

## Type of Change

<!-- Use the checkboxes [x] on the options that are relevant. -->

- [ ] Update to CI Environment or utilities (Non-module affecting
changes)
- [x] Azure Verified Module updates:
- [ ] Bugfix containing backwards-compatible bug fixes, and I have NOT
bumped the MAJOR or MINOR version in `version.json`:
- [ ] Someone has opened a bug report issue, and I have included "Closes
#{bug_report_issue_number}" in the PR description.
- [ ] The bug was found by the module author, and no one has opened an
issue to report it yet.
- [x] Feature update backwards compatible feature updates, and I have
bumped the MINOR version in `version.json`.
- [ ] Breaking changes and I have bumped the MAJOR version in
`version.json`.
  - [x] Update to documentation

## Checklist

- [x] I'm sure there are no other open Pull Requests for the same
update/change
- [x] I have run `Set-AVMModule` locally to generate the supporting
module files.
- [x] My corresponding pipelines / checks run clean and green without
any errors or warnings

<!-- Please keep up to date with the contribution guide at
https://aka.ms/avm/contribute/bicep -->

---------

Co-authored-by: Nate Arnold <[email protected]>