Add detailed IP allowlisting explanation for all Git providers

[vim-zz]

✨ PR Description

Purpose and impact: This PR adds detailed information about IP allowlisting for gitStream across GitHub, GitLab, and Bitbucket installations.

Main changes:

• Explains the importance of IP allowlisting for webhook event handling and CI runner requests
• Recommends adding LinearB/gitStream service IPs and using self-hosted runners with static IPs
• Provides context on potential IP-related errors and how to resolve them

Generated by LinearB AI and added by gitStream.
_{AI-generated content may contain inaccuracies. Please verify before using. We'd love your feedback! 🚀}

[orca-security-us]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Infrastructure as Code	0   0   0   0	View in Orca
Passed	SAST	0   0   0   0	View in Orca
Passed	Secrets	0   0   0   0	View in Orca
Passed	Vulnerabilities	0   0   0   0	View in Orca

[gitstream-cm]

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Review dismissed

[gitstream-cm]

Suggested change

	=== "Self-Managed Runners - Kubernetes"
	**Self-Managed Runners**
	First, [register the runner](https://docs.gitlab.com/runner/register/){:target="_blank"} with a tag, and use the named tag in the `.gitlab-ci.yml` file
	**Kubernetes executors**
	1. Ensure your runner configuration (`config.toml` for example) has the followig:
	``` yaml
	[runners.kubernetes]
	=== "Self-Managed Runners - Kubernetes"
	**Self-Managed Runners**
	First, [register the runner](https://docs.gitlab.com/runner/register/){:target="_blank"} with a tag, and use the named tag in the `.gitlab-ci.yml` file
	**Kubernetes executors**
	1. Ensure your runner configuration (`config.toml` for example) has the following:
	```yaml
	[runners.kubernetes]

[MishaKav]

lg