[5.x] Add isLog to IncomingEntry

[ngunyimacharia]

This commit introduces the isLog convenience method to check if a Telescope IncomingEntry is of type Log.

This will improve the readability of the code in the application's TelescopeServiceProvider

Before:

Telescope::filter(function (IncomingEntry $entry) {
    if ($this->app->environment('local')) {
        return true;
    }

    return $entry->type === EntryType::LOG;
});

After:

Telescope::filter(function (IncomingEntry $entry) {
    if ($this->app->environment('local')) {
        return true;
    }

    return $entry->isLog();
});