Update the UI to not expose the Github PAT in the Namespace Admin page

Currently, in the UI, we fetch and display the Github PAT in the namespace admin page. This is not required, as the PAT is not used in the UI for any operations. Also, this is not a secure practice. The following steps are needed to fix this:

1. Do not fetch the Github PAT and do not display it in the UI.

2. Also, do not autofill the Github PAT in the form to edit the repository config. If no PAT is provided in the edit form, then the PAT should not be updated in the secure store.

3. During creation of the repository config, the PAT must be mandatory (as it is currently), however during edits to the repository config the PAT must be optional.