Check if devfile event name is a string during workspace creation

MR: Pending

Description

When creating a workspace, we validate the devfile and enforce certain restrictions on it. As part of that, we are checking if the command name in the events are starting with a restricted prefix. However, we cannot rely on user data. We should first check if it is a string. If not, we should append the error. We should only check if the name starts with a restricted prefix if it is a string. Else, we run into issues like this - https://new-sentry.gitlab.net/organizations/gitlab/issues/1755678/?project=3 .

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