Add Counter.dev analytics support (#988)

### Prerequisites

Put an `x` into the box(es) that apply:

- [ ] This pull request fixes a bug.
- [x] This pull request adds a feature.
- [ ] This pull request introduces breaking change.

### Description

Add Counter.dev analytics support

### Issues Resolved

no support for Counter.dev

### Checklist

Put an `x` into the box(es) that apply:

#### General

- [x] Describe what changes are being made

Added support for Counter.dev analytics. more info at
https://counter.dev/

- [x] Explain why and how the changes were necessary and implemented
respectively

Currently Counter.dev is not supported in the theme. By adding this new
analytics option users no longer need to fork and add it independently.

- [ ] Reference issue with `#<ISSUE_NO>` if applicable

#### Resources

- [ ] If you have changed any SCSS code, run `make release` to
regenerate all CSS files

#### Contributors

- [ ] Add yourself to `CONTRIBUTORS.md` if you aren't on it already

Co-authored-by: Luiz F. A. de Prá <luizdepra@users.noreply.github.com>