fix: add support for multiple hostnames

[stasadev]

The Issue

From Discord: https://discord.com/channels/664580571770388500/1326111991642718301

external_links don't work properly when you have additional_hostnames or additional_fqdns.

ddev-playwright/docker-compose.playwright.yaml

Lines 36 to 37 in 26520ac

	external_links:
	- ddev-router:${DDEV_HOSTNAME}

 external_links: 
   - "ddev-router:${DDEV_HOSTNAME}"

It is expanded with an invalid syntax:

 external_links: 
   - "ddev-router:primary.ddev.site,secondary.ddev.site"

It should look like this:

 external_links: 
   - "ddev-router:primary.ddev.site"
   - "ddev-router:secondary.ddev.site"

How This PR Solves The Issue

Uses go templates to create the correct external_links in .ddev/docker-compose.playwright_extras.yaml

Manual Testing Instructions

This allows for example to have Mailpit to work automatically without any port change.

mkdir playwright-test && cd playwright-test
ddev config --additional-fqdns="hello.test" --additional-hostnames "extra1,extra2,more.extra"
echo '<?php echo "Hello World;"; ?>' > index.php
ddev add-on get https://github.com/stasadev/ddev-playwright/tarball/20250107_stasadev_external_links

cat .ddev/docker-compose.playwright_extras.yaml
#ddev-generated
services:
  playwright:
    external_links:
      - "ddev-router:${DDEV_PROJECT}.${DDEV_TLD}"
      - "ddev-router:extra1.${DDEV_TLD}"
      - "ddev-router:extra2.${DDEV_TLD}"
      - "ddev-router:hello.test"
      - "ddev-router:more.extra.${DDEV_TLD}"

ddev start

cat .ddev/.ddev-docker-compose-full.yaml
        external_links:
            - ddev-router:playwright-test.ddev.site
            - ddev-router:extra1.ddev.site
            - ddev-router:extra2.ddev.site
            - ddev-router:hello.test
            - ddev-router:more.extra.ddev.site

Related Issue Link(s)

• fix: add support for multiple hostnames tyler36/ddev-cypress#54

[julienloizelet]

Thanks for the PR!