CHEF-29311 - Remove SLA from README

[nandanhegde73]

This pull request removes the oft-misleading Chef SLA text from the README.md file. This action is being taken as part of the 2025 Repo Standardization Initiative. As Progress Chef makes a best effort to respond to issues and pull requests in a timely manner, and prioritizes bugfixes and security updates on a customer-driven basis (which may span repos, or have no repo footprint at all), we no longer support the concept of a Service Level Agreement (SLA) on a repository-centric basis. For further details, see Repo SLA Removal FAQ.

[netlify[bot]]

👷 Deploy Preview for chef-server processing.

Name	Link
🔨 Latest commit	3120e5b08fad469d872a7b288bb98ca894a85c1c
🔍 Latest deploy log	https://app.netlify.com/projects/chef-server/deploys/693f67960a0eae00085e1931

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud