chore: Update v1.16 change files

[SarahFrench]

I mentioned that I thought the v1.16 change log could be cleaned up, so instead of leaving it at that here are some proposed changes. My understanding is that in the past, before changie was introduced for changelog generation, it was usual for an engineer to edit the changelog of a new release and introduce consistency then. This PR serves the same purpose.

To get these results I:

• Explored the change files for v1.16 and identified some easy changes to make:
  • Consistent 'enhancement' type for adding -json support.
• Used an agent to analyse changelogs for v1.0 to the present day v1.16 changelog and propose a style guide for the entries.
  • During this process I:
    • Emphasised user-facing language is important
    • Chose to standardise on active voice over passive voice, and use present tense
    • Chose consistent use of backticks to format flags/block names/identifiers.
    • Specified to use sentence case
    • Specified to use a prefix if a change is scoped to a specific command or backend implementation.
• Started a new agent session and tasked that agent with using the style guide to propose changes to the change files for v1.16.
• For each proposed change I manually reviewed and accepted/rejected proposed changes. For example, some of the actions-related changes were going to mistakenly have a stacks: prefix added.

As team we need to agree on any skills etc used to enforce a style guide on our changelog, and when this was previously discussed interest was low. Therefore this PR is not introducing a style guide, it is only proposing changes to the v1.16 change files based on an initial version of that style guide.

We can merge this PR or just use it as the start of discussions - happy for whatever.

Target Release

1.16.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.