[EC-323] Fix error when getting the first letters on avatar image creation

[fedemkr]

Type of change

• Bug fix
• New feature development
• Tech debt (refactoring, code cleanup, dependency upgrades, etc)
• Build/deploy pipeline (DevOps)
• Other

Objective

Fix getting the first letters on avatar image creation. There are some cases when more spaces are added, at the beginning, at the end or in the middle that causes the method to fail.

Code changes

• AvatarImageSource.cs: Sanitized data on getting first letters so that it doesn't fail when more spaces are added

Before you submit

• I have checked for formatting errors (dotnet tool run dotnet-format --check) (required)
• I have added unit tests where it makes sense to do so (encouraged but not required)
• This change requires a documentation update (notify the documentation team)
• This change has particular deployment requirements (notify the DevOps team)

[vvolkgang]

We might have to revisit this but let's merge the fix for now!