CLOUDP-277156: [API Platform] Validate exemptions

[andreaangiolillo]

Proposed changes

Jira ticket: CLOUDP-277156

This PR updates the foas breaking-changes exemptions parse command to always validate the exemption file.

Before

./bin/foascli breaking-changes exemptions parse --exemption-file ~/Downloads/exemptions.yaml --ignore-expiration

2024/12/12 15:17:54 Generating exemptions from file in /Users/andrea.angiolillo/Downloads/exemptions.yaml
2024/12/12 15:17:54 Found 1251 valid exemptions
2024/12/12 15:17:54 Exemptions file generated in exemptions.txt

After

foascli breaking-changes exemptions parse --exemption-file ~/Downloads/exemptions.yaml --ignore-expiration                            

2024/12/12 16:18:39 Generating exemptions from file in /Users/andrea.angiolillo/Downloads/exemptions.yaml
Error: could not get valid exemptions list: validation error: parsing time "20240810" as "2006-01-02": cannot parse "0810" as "-". Exemption: {API None None removed the schema 'ClusterDescription20240710' [api-schema-removed] 20240810 Exemption for cloud-dev only, generated as a result of un-hiding the new version in cloud-dev true}