Uptade documentation with new energy storage investment option

[datejada]

Pull request details

Describe the changes made in this pull request

As part of the changes in epic #575, this PR updates the documentation in the formulation and how-to sections.

List of related issues or pull requests

Closes #628

Collaboration confirmation

As a contributor I confirm

• [x] I read and followed the instructions in README.dev.md
• [x] The documentation is up to date with the changes introduced in this Pull Request (or NA)
• [x] Tests are passing
• [x] Lint is passing