feat: simplify plugin usage

[macklinu]

Resolves #45

BREAKING CHANGE: This removes some options and has some modified behavior.

• automatically checks for JIRA keys in the PR title and branch name (no config needed)
• only reports unique JIRA keys (if the same one is found in the PR title and branch, only report that once)
• remove emoji and location options
• simplify format() option signature

TODO:

• check for JIRA keys in the commit message titles