Exclude extra release notes from Spelling/Term checks.
Exclude `<a>` from checks.
Add new terms and fix some double space errors.
- Before: 2691
- After: 967
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## Description
As per https://docker.atlassian.net/browse/ENGDOCS-2836
Next up:
- tidy up/ split the security FAQs
- move the 'for developers' content up one level
- beef up the Deploy DD page
- AOB
(didn't want to include in this PR as it's already too long)
## Reviews
<!-- Notes for reviewers here -->
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- [ ] Technical review
- [ ] Editorial review
- [ ] Product review