fix: add support for multiple hostnames

[stasadev]

The Issue

• Closes Update readme to include instructions for additional hostnames. #52

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

ddev-selenium-standalone-chrome/docker-compose.selenium-chrome.yaml

Lines 20 to 21 in d11aaf3

	external_links:
	- ddev-router:${DDEV_SITENAME}.${DDEV_TLD}

 external_links: 
   - "ddev-router:${DDEV_SITENAME}.${DDEV_TLD}"

It works only for the main URL, but not for additional URLs.

How This PR Solves The Issue

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

Manual Testing Instructions

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

mkdir selenium-chrome-test && cd selenium-chrome-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/ddev/ddev-selenium-standalone-chrome/tarball/20250107_stasadev_external_links

cat .ddev/docker-compose.selenium-chrome_extras.yaml
#ddev-generated
services:
  selenium-chrome:
    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:selenium-chrome-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