Add a docs page to explain NGINX Agent features #4408

Job	Run time
Build Grafana Dashboard Example	53s
Build signed snapshot	6m 23s
Component Tests	44s
Build unsigned snapshot	3m 33s
Lint	33s
Performance Tests	7m 9s
Unit Tests	3m 18s
Integration Tests (rockylinux, 8)	4m 29s
Integration Tests - Official OSS Images (bookworm, stable, debian)	3m 44s
Integration Tests (rockylinux, 9)	5m 6s
Integration Tests - Official Plus Images (alpine, 3.20, r32, alpine, /nginx-plus/agent)	3m 53s
Integration Tests - Official OSS Images (bookworm, mainline, debian)	3m 41s
Integration Tests (almalinux, 8)	4m 19s
Integration Tests - Official Plus Images (alpine, 3.19, r31, alpine, /nginx-plus/agent)	3m 53s
Integration Tests - Official OSS Images (alpine, stable, alpine)	3m 28s
Integration Tests (almalinux, 9)	3m 47s
Integration Tests - Official Plus Images (debian, bookworm, r32, debian, /nginx-plus/agent)	3m 46s
Integration Tests - Official OSS Images (alpine, mainline, alpine)	3m 46s
Integration Tests (amazonlinux, 2)	4m 13s
Integration Tests - Official Plus Images (debian, bookworm, r31, debian, /nginx-plus/agent)	4m 6s
Integration Tests (amazonlinux, 2023)	3m 49s
Integration Tests (oraclelinux, 8)	5m 4s
Integration Tests (oraclelinux, 9)	4m 17s
Integration Tests (ubuntu, 24.04)	3m 15s
Integration Tests (alpine, 3.17)	2m 44s
Integration Tests (alpine, 3.18)	2m 48s
Integration Tests (alpine, 3.19)	2m 34s
Integration Tests (alpine, 3.20)	2m 35s
Integration Tests (debian, bullseye-slim)	3m 48s
Integration Tests (debian, bookworm-slim)	2m 51s
trigger-release-workflow	0s
	1h 48m 29s

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