Update Reports to include TLP:AMber markings

[aloftus23]

fixes #310

🗣 Description

Adds the TLP:AMBER flag to the mailer and style.css was updated to conform to the template changes. *The HTML templates are not uploaded to GitHub, but can be requested by reaching out to a P&E team member.

💭 Motivation and context

Follows the CISA TLP Guidelines.

🧪 Testing

Passes pre-commit and pytests.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.

[dav3r]

I'm not sure if you are aware of this or if you planned to do it later, but either way I wanted to mention/remind that we don't review PRs until all of the items in the "Pre-approval checklist" have either been checked or removed (if they don't apply to this PR).

[coveralls]

Coverage: 25.555%. Remained the same when pulling e4a123f on AL-add-tlpAmber into d3d7439 on develop.

[dav3r]

👍 👍

[cduhn17]

Looks good