Fix Searxng not working out of the box

[adivardhan1000]

Pull Request Title: [Short Description of Changes]

Description

This PR solves two issues:

1. As the title suggests, searxng doesn't work out of the box and keeps crashing. This is because it looks for a default settings.yml and tries to mount it to /etc/searxng. The docker keeps crashing since settings.yml is not present.
2. The tailnet name should be a .env variable.

Type of Change

• Bug fix
• Refactoring

How Has This Been Tested?

Have deployed on my server successfully.

Checklist

• I have performed a self-review of my code
• I have added tests that prove my fix or feature works
• I have updated necessary documentation (e.g. frontpage README.md)
• Any dependent changes have been merged and published in downstream modules

Additional Notes

I am not sure if this is the best pattern to put settings.yml but wanted to create a PR to start a discussion for the best way forward.

[jackspiering]

Looks good to me. @crypt0rr could you also do a review please? If it looks good to you, please approve and merge 👍

[jackspiering]

@adivardhan1000 please fix the linting error: "./services/searxng/README.md:13:42 MD034/no-bare-urls Bare URL used [Context: "https://github.com/searxng/sea..."]"