headerHeight auto no longer works due to number transform

[alessaro92]

After the merge of PR #2228, which includes commit 1e883ea, the headerHeight input property is now transformed to a number.

This change breaks existing code that relied on the "auto" option for dynamic header height adjustment, for example:
[headerHeight]="$any('auto')"

Previously, setting headerHeight to auto allowed the header height to automatically adjust based on the content of the header cells.
Now, since the input is forced through a number transform, the string "auto" is converted to a falsy value, which causes the header not to render at all (because its visibility depends on headerHeight being truthy).

The issue #2048 also mentions that there are parts of the component logic that explicitly check whether headerHeight is a string and whether it equals "auto".