* Move EventSource to SharedWorker (#12095)

Backport #12095

Move EventSource to use a SharedWorker. This prevents issues with HTTP/1.1
open browser connections from preventing gitea from opening multiple tabs.

Also allow setting EVENT_SOURCE_UPDATE_TIME to disable EventSource updating

Fix #11978

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

* Bugfix for shared event source

For some reason our eslint configuration is not working correctly
and a bug has become apparent when trying to backport this to 1.12.

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Re-fix #12095 again

Unfortunately some of the suggested changes to #12095 introduced
bugs which due to caching behaviour of sharedworkers were not caught
on simple tests.

These are as follows:

* Changing from simple for loop to use includes here:

```js
  register(port) {
    if (!this.clients.includes(port)) return;

    this.clients.push(port);

    port.postMessage({
      type: 'status',
      message: `registered to ${this.url}`,
    });
  }
```

The additional `!` prevents any clients from being added and should
read:

```js
    if (this.clients.includes(port)) return;
```

* Dropping the use of jQuery `$(...)` selection and using DOM
`querySelector` here:

```js
async function receiveUpdateCount(event) {
  try {
    const data = JSON.parse(event.data);

    const notificationCount = document.querySelector('.notification_count');
    if (data.Count > 0) {
      notificationCount.classList.remove('hidden');
    } else {
      notificationCount.classList.add('hidden');
    }

    notificationCount.text() = `${data.Count}`;
    await updateNotificationTable();
  } catch (error) {
    console.error(error, event);
  }
}
```

Requires that `notificationCount.text()` be changed to use `textContent`
instead.

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

Should eliminate a error in the Firefox console regarding the connection
being interrupted while the page was loading.

If the browser supports EventSource switch to use this instead of
polling notifications.

Signed-off-by: Andrew Thornton art27@cantab.net

* Use AJAX for notifications table

Signed-off-by: Andrew Thornton <art27@cantab.net>

* move to separate js

Signed-off-by: Andrew Thornton <art27@cantab.net>

* placate golangci-lint

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Add autoupdating notification count

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Fix wipeall

Signed-off-by: Andrew Thornton <art27@cantab.net>

* placate tests

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Try hidden

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Try hide and hidden

Signed-off-by: Andrew Thornton <art27@cantab.net>

* More auto-update improvements

Only run checker on pages that have a count
Change starting checker to 10s with a back-off to 60s if there is no change

Signed-off-by: Andrew Thornton <art27@cantab.net>

* string comparison!

Signed-off-by: Andrew Thornton <art27@cantab.net>

* as per @silverwind

Signed-off-by: Andrew Thornton <art27@cantab.net>

* add configurability as per @6543

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Add documentation as per @6543

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Use CSRF header not query

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Further JS improvements

Fix @etzelia update notification table request
Fix @silverwind comments

Co-Authored-By: silverwind <me@silverwind.io>
Signed-off-by: Andrew Thornton <art27@cantab.net>

* Simplify the notification count fns

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: silverwind <me@silverwind.io>