Add configuration for UNLEASH_URL to values file

[mattiasbpersson]

Describe the feature request

We missed how we should configure the UNLEASH_URL to get the slack-notification working. We found that documentations for it and gave it a try.

Would be great is this is included in the values file too:
https://docs.getunleash.io/using-unleash/deploy/configuring-unleash#unleash-url

The same for
UNLEASH_DEFAULT_ADMIN_USERNAME
UNLEASH_DEFAULT_ADMIN_PASSWORD

Background

No response

Solution suggestions

https://github.com/Unleash/helm-charts/blob/main/charts/unleash/values.yaml#L64C1-L68C58

env: []
#  - name: UNLEASH_URL
#    value: <Should be set to the public discoverable URL of your instance, so if your instance is accessed by your users >
#  - name: UNLEASH_DEFAULT_ADMIN_USERNAME
#    value: The initial admin username
#  - name: UNLEASH_DEFAULT_ADMIN_PASSWORD
#    value: The initial admin password

[gastonfournier]

Hi @mattiasbpersson it seems reasonable, please feel free to open a PR suggesting that change.