feat: add validation for object-format flag in repo create command (#741)

This PR adds validation for the `--object-format` flag in the `repo create` command. The flag now accepts only `sha1` or `sha256` as valid values, and returns an error for any other value.

Changes:
- Added validation in `runRepoCreate` to check for valid object format values
- Added unit tests to verify the validation logic
- Fixed the field name from `ObjectFormat` to `ObjectFormatName` to match the SDK

The changes ensure that users get clear error messages when using invalid object format values, improving the user experience.

Fix #727
Fix #660
Fix #767

Co-authored-by: techknowlogick <techknowlogick@noreply.gitea.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/741
Reviewed-by: TheFox0x7 <thefox0x7@noreply.gitea.com>

docs/CLI.md

@@ -1071,6 +1071,8 @@ Create a repository
 
 **--name, -**="": name of new repo
 
+**--object-format**="": select git object format (sha1,sha256)
+
 **--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
 
 **--owner, -O**="": name of repo owner