Adds sitemap enabled to Feed Me

[ishetnogferre]

Description

This PR adds the field for "Sitemap Enabled" in feedme.

Caveat

This PR only adds the field, but it doesn't allow it yet to be imported. That still gets blocked by the "override" option.
For the robots field, it just worked out of the box, so I compared the processing of those two and found this to be the difference:

In Sitemap.php in processing the metaSiteMapVars the inherited are removed.

$attributes = $fieldMetaBundle->metaSitemapVars->getAttributes();
$inherited = array_keys(ArrayHelper::remove($attributes, 'inherited', []));
$attributes = array_intersect_key($attributes, array_flip((array)$seoSettingsField->sitemapEnabledFields));
$attributes = array_filter($attributes, [ArrayHelper::class, 'preserveBools']);
foreach ($inherited as $inheritedAttribute) {
    unset($attributes[$inheritedAttribute]);
}
$metaBundle->metaSitemapVars->setAttributes($attributes, false);

But in later in Sitemap.php in processing the metaGlobalVars they aren't.

$attributes = $fieldMetaBundle->metaGlobalVars->getAttributes();
$attributes = array_filter(
    $attributes,
    [ArrayHelper::class, 'preserveBools']
);
$metaBundle->metaGlobalVars->setAttributes($attributes, false);

Solution

The solution is more a business decision on the plugin part where to solve this: in the processing part or in feed-me.
Also I couldn't yet estimate the impact on our code so for a quick-fix, I added the Override field as well and that works.

		{
			label: 'Override Sitemap Enabled',
			handle: 'override-sitemapUrls',
			default: {
				type: 'select',
				options: [
					{ label: 'Don\'t import'|t('feed-me'), value: '' },
					{ label: 'Override (use imported value)', value: '1' },
					{ label: 'Inherit (ignore imported value)', value: '0' },
				],
			}
		},

Related issues

A request for this feature already existed in: #1070

[khalwat]

Thanks for the PR, I'll have a look at the issue you raised as well.