Update documentation to include all templaters

[timchurch]

Brief summary of the change made

Minor documentation updates to clearly illustrate all available templaters supported by SQLFluff.

Also fixes one minor Markdown formatting issue.

Are there any other side effects of this change that we should be aware of?

No

Pull Request checklist

• Please confirm you have completed any of the necessary steps below.

• Included test cases to demonstrate any code changes, which may be one or more of the following:

  • .yml rule test cases in test/fixtures/rules/std_rule_cases.
  • .sql/.yml parser test cases in test/fixtures/dialects (note YML files can be auto generated with tox -e generate-fixture-yml).
  • Full autofix test cases in test/fixtures/linter/autofix.
  • Other.

• Added appropriate documentation for the change.

• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[github-actions]

Coverage Results ✅

Name    Stmts   Miss  Cover   Missing
-------------------------------------
TOTAL   17741      0   100%

225 files skipped due to complete coverage.

[coveralls]

coverage: 99.985%. remained the same
when pulling 1bca343 on timchurch:documentation-include-all-templaters
into 1d4fd8d on sqlfluff:main.

[WittierDinosaur]

LGTM