Custom Meta tags: Allow - in the machine name of the tag

The PR is ready for review

The PR looks like it can handle <meta name="format-detection" content="telephone=no"> now which is great. Can you also update it so colons are allowed? In my case I need to add twitter:data1 meta tags

Updated the scope of the bug as per #note-5

@sagesolutions Please file a separate bug for it

Thank you for working on this.

In hindsight I think we should have transparently converted the name of the meta tag from a user entered string to something for the machine name, to avoid situations where meta tag names just don't match the limitations of the machine name logic.

That said, thank you for the improvements.

A few minor nitpicks:

     $form['id'] = [
       '#type' => 'machine_name',
+      '#maxlength' => 64,
+      '#description' => $this->t('A unique name for this custom tag. Must be alpha-numeric, hyphen, or underscore separated.'),

+  protected function createCustomMetaTag($id, $label, $description, $htmlElement, $htmlNameAttribute, $htmlValueAttribute) {
+    // Access custom meta add page.
+    $this->drupalGet('admin/config/search/metatag/custom-tags/add');
+    $this->assertSession()->statusCodeEquals(200);
+    $edit = [];
+    $edit['id'] = $id;
+    $edit['label'] = $label;
+    $edit['description'] = $description;
+    $edit['htmlElement'] = $htmlElement;
+    $edit['htmlNameAttribute'] = $htmlNameAttribute;
+    $edit['htmlValueAttribute'] = $htmlValueAttribute;
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->addressEquals('/admin/config/search/metatag/custom-tags');
+    $this->assertSession()->pageTextContains('Created Format Detection Custom tag.');
+  }

The pageTextContains() check has the name of one meta tag hardcoded, it should check for the $label.

Accomodated #note-9

This would be accommodated in 💬 Creating custom meta tag Active

adding temporary patch allowing colons ":" inside machine name, waiting the relataed issue to be resolved

Ok it seems there is a problem wiith the config entity to have colons inside theire name. So it would be better if we can split the machine name of config and also the real name of the tag?