Add default values for global.kas.service.apiExternalPort

What does this MR do?

We currently doesn't set global.kas.service.apiExternalPort by default in the values.yaml file. If we set global.kas.enabled to true without setting this value, helm install will fail with the following error:

Error: template: gitlab/charts/gitlab/charts/webservice/templates/deployment.yaml:53:28: executing "gitlab/charts/gitlab/charts/webservice/templates/deployment.yaml" at <include (print $.Template.BasePath "/configmap.yml") $>: error calling include: template: gitlab/charts/gitlab/charts/webservice/templates/configmap.yml:117:10: executing "gitlab/charts/gitlab/charts/webservice/templates/configmap.yml" at <include "gitlab.appConfig.kas" .>: error calling include: template: gitlab/charts/gitlab/templates/_gitlab.yaml.tpl:39:19: executing "gitlab.appConfig.kas" at <include "gitlab.appConfig.kas.internalUrl" .>: error calling include: template: gitlab/charts/gitlab/templates/_kas.tpl:47:24: executing "gitlab.appConfig.kas.internalUrl" at <.Values.global.kas.service.apiExternalPort>: nil pointer evaluating interface {}.apiExternalPort

Another fix is to set the default value in charts/gitlab/templates/_kas.tpl if global.kas.service.apiExternalPort is not set.

Related issues

Customer reported this issue: https://gitlab.zendesk.com/agent/tickets/209752 (internal)

Checklist

See Definition of done.

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Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened