Pull Request resolves # .

Summary of Changes

This PR turns the Update Site edit form (com_installer → Update Sites → edit) into a full editor for the #__update_sites.extra_query column.

Until now the edit form exposed a single Download Key text field, and only for extensions whose manifest declares a <dlid> element (for every other update site the field was
removed entirely). There was no way to view or edit the complete extra_query string, nor to add additional custom query parameters that some update servers require.

The Download Key text field is replaced by a repeatable subform where each row is a key_name / key_value pair. On save the rows are serialised back into the standard
query-string format key1=value1&key2=value2&... and stored in #__update_sites.extra_query; on load the stored string is parsed back into rows. The subform is now available for
all update sites, not only download-key extensions.

Note: this changes the download-key editing UX. Previously the manifest <dlid prefix="…" suffix="…"> was used to auto-wrap the value the user typed (e.g. the user entered only the token and Joomla stored dlid=TOKEN). With the generic key/value subform the administrator now edits the raw parameters directly (e.g. they type dlid / TOKEN), so the <dlid> prefix/suffix are no longer applied on this screen. <dlid> is still used elsewhere (Update Sites list "download key" status column, the Update view, and the supported/exists-key filters), so the flag itself keeps working.

Testing Instructions

1. Have a Joomla installation with at least one installed extension that has an update server (any extension works; a paid extension declaring <dlid> is ideal for the download-key case).
2. Go to System → Update → Update Sites (index.php?option=com_installer&view=updatesites).
3. Click an update site name to open the edit form.
4. Add one or more rows in the Extra Query Parameters subform, e.g. dlid / abcdef123456 and foo / bar.
5. Save & Close, then reopen the same update site.
6. Optionally inspect the database: SELECT extra_query FROM #__update_sites WHERE update_site_id = ….

Actual result BEFORE applying this PR

• The edit form shows a single Download Key text field, and only for extensions whose manifest declares <dlid>.
• For all other update sites there is no editable field for extra_query at all.
• It is not possible to add arbitrary extra query parameters to an update server URL.

Expected result AFTER applying this PR

• The edit form shows an Extra Query Parameters repeatable subform for every update site.
• Each row is a key_name / key_value pair; multiple rows can be added or removed.
• On save, the rows are stored in #__update_sites.extra_query as key1=value1&key2=value2&...; reopening the form shows the same rows.
• The stored extra_query is appended to the update server URL exactly as before, so update checks and downloads keep working.