chore(changelog): fixup git-cliff formatting (#1214)

- Replaced backticks surrounding body with blockquotes. This formats
  significantly better.
- Added a few postprocessors to remove junk like the PR template,
  horizontal lines and some trailing whitespace

---

Note: there is extra non-automatically generated stuff in the changelog
that this would remove - the changes to CHANGELOG.md should not be
merged as-is, and this is worth waiting for @orhun to check out.

Compare:
5e7fbe8c32/CHANGELOG.md
To: https://github.com/ratatui-org/ratatui/blob/main/CHANGELOG.md

---------

Co-authored-by: Orhun Parmaksız <orhunparmaksiz@gmail.com>

cliff.toml

@@ -31,16 +31,14 @@ body = """
   {% if commit.github.username %} by @{{ commit.github.username }}{%- endif -%}\
   {% if commit.github.pr_number %} in [#{{ commit.github.pr_number }}]({{ self::remote_url() }}/pull/{{ commit.github.pr_number }}){%- endif %}\
 {%- if commit.breaking %} [**breaking**]{% endif %}
-{%- if commit.body %}
-
-  ````text {#- 4 backticks escape any backticks in body #}
-  {{commit.body | indent(prefix="  ") }}
-  ````
+{%- if commit.body %}\n\n{{ commit.body | indent(prefix="  > ", first=true, blank=true) }}
 {%- endif %}
-{%- for footer in commit.footers %}
+{%- for footer in commit.footers %}\n
 {%- if footer.token != "Signed-off-by" and footer.token != "Co-authored-by" %}
-
-  {{ footer.token | indent(prefix="  ") }}{{ footer.separator }}{{ footer.value }}
+  >
+{{ footer.token | indent(prefix="  > ", first=true, blank=true) }}
+{{- footer.separator }}
+{{- footer.value| indent(prefix="  > ", first=false, blank=true)  }}
 {%- endif %}
 {%- endfor %}
 {% endmacro -%}
@@ -87,6 +85,11 @@ trim = false
 footer = """
 <!-- generated by git-cliff -->
 """
+postprocessors = [
+  { pattern = '<!-- Please read CONTRIBUTING.md before submitting any pull request. -->', replace = "" },
+  { pattern = '>---+\n', replace = '' },
+  { pattern = ' +\n', replace = "\n" },
+]
 
 [git]
 # parse the commits based on https://www.conventionalcommits.org
@@ -126,6 +129,7 @@ commit_parsers = [
   { message = "^(Buffer|buffer|Frame|frame|Gauge|gauge|Paragraph|paragraph):", group = "<!-- 07 -->Miscellaneous Tasks" },
   { message = "^\\[", group = "<!-- 07 -->Miscellaneous Tasks" },
 ]
+
 # protect breaking changes from being skipped due to matching a skipping commit_parser
 protect_breaking_commits = false
 # filter out the commits that are not matched by commit parsers