Fix doctring log-likelihood to distribution, Fix for issue #7563

[aibit0111]

Replaced all the "log-likelihood" with "distribution" in multivariate.py file

Description

Updated the docstrings for better clarity. Replaced "log-likelihood" with "distribution" to accurately describe the functionality, as the class provides more than just log-likelihood, including cdf, mean, and random methods.

Related Issue

• Closes Docstrings of distributions should not read x log-likelihood #7563
• Related to #

Checklist

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

Type of change

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

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📚 Documentation preview 📚: https://pymc--7576.org.readthedocs.build/en/7576/

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