WPB-14284 personal user invitation URL configmap fixed

[battermann]

https://wearezeta.atlassian.net/browse/WPB-14284

This in combination with the caillaich PR https://github.com/zinfra/cailleach/pull/2380 should fix the setting for the team invitation URL for personal users.

The brig server configs in some environments have the field emailSMS.team set, in which case the invitation URL set there as tExistingUserInvitationUrl. If emailSMS.team does not exist, the URL is constructed from externalUrls.accountPages.

So depending on the environment, a correct config must contain either a value for emailSMS.team.tExistingUserInvitationUrl or for externalUrls.accountPages.

Checklist

• Merge the cailleach PR first
• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[pcapriotti]

LGTM