Add a docs page to explain NGINX Agent features #4407

Job	Run time
Component Tests	45s
Build signed snapshot	6m 26s
Build unsigned snapshot	3m 33s
Build Grafana Dashboard Example	45s
Lint	24s
Performance Tests	7m 13s
Unit Tests	3m 20s
Integration Tests (rockylinux, 8)	3m 53s
Integration Tests (rockylinux, 9)	4m 54s
Integration Tests - Official Plus Images (alpine, 3.20, r32, alpine, /nginx-plus/agent)	3m 46s
Integration Tests (almalinux, 8)	3m 46s
Integration Tests - Official OSS Images (bookworm, stable, debian)	3m 48s
Integration Tests - Official Plus Images (alpine, 3.19, r31, alpine, /nginx-plus/agent)	3m 36s
Integration Tests (almalinux, 9)	3m 35s
Integration Tests - Official OSS Images (bookworm, mainline, debian)	3m 47s
Integration Tests (amazonlinux, 2)	4m 17s
Integration Tests - Official Plus Images (debian, bookworm, r32, debian, /nginx-plus/agent)	3m 36s
Integration Tests - Official OSS Images (alpine, stable, alpine)	3m 40s
Integration Tests - Official Plus Images (debian, bookworm, r31, debian, /nginx-plus/agent)	3m 42s
Integration Tests (amazonlinux, 2023)	4m 6s
Integration Tests - Official OSS Images (alpine, mainline, alpine)	3m 37s
Integration Tests (oraclelinux, 8)	5m 18s
Integration Tests (oraclelinux, 9)	4m 14s
Integration Tests (ubuntu, 24.04)	3m 17s
Integration Tests (alpine, 3.17)	2m 39s
Integration Tests (alpine, 3.18)	2m 31s
Integration Tests (alpine, 3.19)	2m 45s
Integration Tests (alpine, 3.20)	2m 29s
Integration Tests (debian, bullseye-slim)	3m 0s
Integration Tests (debian, bookworm-slim)	3m 4s
trigger-release-workflow	0s
	1h 45m 46s

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