Update the changelog template

[yhaliaw]

Applicable spec:

Overview

Updated the changelog template

Rationale

The previous Checklist was not clear on:

• Where the changelog is located
• What type of changes should be recorded
• What is the format of the changelog

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, senior-review-required, documentation)
• The changelog is updated.

[github-actions]

Test results for commit 1551697

Test coverage for 1551697

Name           Stmts   Miss Branch BrPart  Cover   Missing
----------------------------------------------------------
src/charm.py      31      0      4      0   100%
----------------------------------------------------------
TOTAL             31      0      4      0   100%

Static code analysis report

Run started:2025-03-06 02:12:30.957979

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 151
  Total lines skipped (#nosec): 0
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):

[yanksyoon]

Would adding the initial changelog be good here? (or appending this change to the changelog?)

[seb4stien]

Not sure if it would work: maybe you could directly create a link to the changelog?