Collections summary does not accept file creation date tags from slug

**Describe the bug**
`collections` `summary` does not accept file creation date tags from slug as mentioned in the [docs](https://www.netlifycms.org/docs/configuration-options/#summary)

**To Reproduce / CMS Configuration**
Use `{{year}}/{{month}}/{{day}} {{hour}}:{{minute}}:{{second}}` in `summary` to see it not work. Also added `commit_date` for reference to make the problem more obvious.

```
collections:
- name: 'page'
label: 'Page'
folder: 'out'
create: true
format: json
extension: 'json'
slug: '{{slug}}_{{year}}{{month}}{{day}}{{hour}}{{minute}}{{second}}'
summary: "{{title}} – by {{commit_author}} on {{year}}/{{month}}/{{day}} {{hour}}:{{minute}}:{{second}} {{commit_date | date('MM/DD/YYYY h:mm:ssA')}}"
fields: ...
```

**Expected behavior**
it displays the values that correspond to the file creation tag.

**Screenshots**

**Applicable Versions:**
- Netlify CMS version: 2.10.192
- Git provider: BitBucket