docs: fix PagerDuty capitalization across provider documentation

[ayoubil]

Fixes #5405.

The product name PagerDuty (capital D) is currently rendered as Pagerduty (lowercase d) across multiple documentation pages. This PR normalizes all user-visible documentation references to the official capitalization.

Changes (10 string replacements across 4 files)

File	Occurrences
docs/providers/overview.mdx	Card title
docs/providers/overview.md	List entry
docs/overview/servicetopology.mdx	Card title
docs/providers/documentation/pagerduty-provider.mdx	frontmatter title + description, body intro, two webhook-section mentions, two "Useful Links" entries

What stays unchanged (out of scope)

• The provider's Python class name PagerdutyProvider and module path pagerduty_provider — renaming would be a breaking API change with cascading effects on user configs, imports, and serialized state.
• The internal kebab-case URL slug pagerduty-provider — already lowercase by convention.
• Existing log messages and Python docstrings (line: OAuth2 callback logic for Pagerduty, etc.) — not user-facing in the docs site, can be a separate cleanup if desired.

Verification

grep -rn 'Pagerduty' docs/    # before: 9 matches; after: 0