[FAU-423] Use <TextControl> for duration of studies

[tyrann0us]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Feature

What is the current behavior? (You can also link to an open issue here)
https://inpsyde.atlassian.net/browse/FAU-423
"Duration of studies in semester" field is a multi-line input (<TextareaControlFormField>).

What is the new behavior (if this is a feature change)?
"Duration of studies in semester" field is a single-line input (<TextControl>).

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
No, existing content will be kept.

Before:

After:

Other information:
There's currently an unrelated error preventing any input (source). However, this shouldn't affect this change (or vice versa).

[amiut]

Thanks for taking care of it, LGTM, left a small (unrelated) suggestion but nothing that prevents me from approving.

[zhyian]

Thanks!