Fix GitLab API connection timeout errors

[rafael7maia]

Problem:
The GitLab client was using the default HTTP client without retry logic or customized timeouts, causing net/http: TLS handshake timeout errors when connecting to GitLab API, especially on slow or unstable network connections.

Solution:
Configure the GitLab client with go-retryablehttp (already used for GitHub client) to handle temporary network issues and increase timeout thresholds:

• TLS handshake timeout: 30 seconds (up from ~10s default)
• Response header timeout: 30 seconds
• Total request timeout: 60 seconds
• Retry policy: up to 5 retries with exponential backoff (2s-30s)

Changes:

• Added retryable HTTP client configuration for GitLab API calls
• Applied same retry pattern already used for GitHub client
• No breaking changes to existing functionality

Testing:
Tested successfully on projects with slow network conditions that previously failed with timeout errors.

References:

• HashiCorp go-retryablehttp: https://github.com/hashicorp/go-retryablehttp
• Similar pattern already implemented for GitHub client in this codebase