Implement icdf() method for Asymmetric Laplace distribution

[darmendariz]

Description

Implement the inverse CDF for Asymmetric Laplace and provide corresponding tests. The functional form of the ICDF was derived by hand based on the CDF given in Wikipedia (Asymmetric Laplace distribution).

Related Issue

• [ ] Closes #
• [x] Related to #6612

Checklist

• [x] Checked that the pre-commit linting/style checks pass
• [x] Included tests that prove the fix is effective or that the new feature works
• [x] Added necessary documentation (docstrings and/or example notebooks)
• [x] If you are a pro: each commit corresponds to a relevant logical change

Type of change

• [x] New feature / enhancement
• [ ] Bug fix
• [ ] Documentation
• [ ] Maintenance
• [ ] Other (please specify):