docs: Update Relay Kit description

[germartinez]

Context

Currently the Relay Kit description mentions ERC-4337 as the only transaction relaying mechanism (implicitly), but we are also supporting Gelato relay.

This PR:

• Adjusts the Relay Kit description.

[github-actions]

Branch preview

✅ Deployed successfully in branch deployment:

https://update_relay_text--docs.review.5afe.dev

[github-actions]

Overall readability score: 38.76 (🔴 -0.03)

File	Readability
overview.mdx	43.13 (🔴 -2.28)
relay-kit.mdx	46.54 (🔴 -3.05)

View detailed metrics

🟢 - Shows an increase in readability
🔴 - Shows a decrease in readability

File	Readability	FRE	GF	ARI	CLI	DCRS
overview.mdx	43.13	32.6	10.84	14.9	16.17	8.06
	🔴 -2.28	🔴 -8.56	🔴 -0.18	🔴 -0.1	🔴 -0.18	🔴 -0.05
relay-kit.mdx	46.54	53.21	12.2	14.2	13.28	8.92
	🔴 -3.05	🔴 -0.2	🔴 -0.57	🔴 -0.5	🔴 -0.52	🔴 -0.18

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	38.76	34.19	12.57	16.58	14.84	8.41
	🔴 -0.03	🔴 -0.06	🟢 +0	🟢 +0	🟢 +0	🟢 +0

View metric targets

Metric	Range	Ideal score
Flesch Reading Ease	100 (very easy read) to 0 (extremely difficult read)	60
Gunning Fog	6 (very easy read) to 17 (extremely difficult read)	8 or less
Auto. Read. Index	6 (very easy read) to 14 (extremely difficult read)	8 or less
Coleman Liau Index	6 (very easy read) to 17 (extremely difficult read)	8 or less
Dale-Chall Readability	4.9 (very easy read) to 9.9 (extremely difficult read)	6.9 or less