Docs: Standardize Dependencies API operation titles and descriptions

What does this MR do?

Standardizes Dependencies API operation titles and descriptions to follow GitLab's RESTful API style guide.

References

Related to: #585399

Changes made

Descriptions standardized:

• List project dependencies: Updated to "Lists all project dependencies for a specified project." to match the title verb. Also fixed grammar: "mirroring" → "mirrors".

Verification

• Titles use approved verbs (List)
• Descriptions start with matching verbs
• Follows Operation titles and Operation descriptions style guide

Type of change

• Documentation only