feat(analyze_org): add --exclude-repo flag to exclude repositories from org scan

[Tyagiquamar]

Problem
When scanning large organizations with poutine analyze_org, users may want to exclude certain repositories from the scan, as requested in #394.

Root Cause / Context
analyze_org scanned all non-archived repositories in an organization without a mechanism to ignore specific repositories by name or identifier.

Fix

• Added ExcludeRepos slice to models.Config with helper method IsRepoExcluded(repoIdentifier, repoName string) bool.
• Added --exclude-repo / -e string slice flag to analyzeOrgCmd and bound it to viper configuration excludeRepos.
• Added exclusion check in AnalyzeOrg before scheduling repository clones and scans, notifying obs.OnRepoSkipped(..., "excluded").

Regression Test

• Added unit tests in models/config_test.go verifying case-insensitive repository identifier and repository name exclusion matching on Config.IsRepoExcluded.

Validation

• go test -v ./models PASS (exit code 0)
• docker run --rm -v ... golang:latest go test -v ./models PASS (exit code 0)

Fixes #394

[fproulx-boostsecurity]

Thanks for the PR! Could you please make sure to run the linter. There is a lint error now https://github.com/boostsecurityio/poutine/actions/runs/37677264023/job/113490130650?pr=458#step:4:35

[Tyagiquamar]

Fixed the errcheck linter finding in commit c4190c6 (_ = viper.BindPFlag("excludeRepos", analyzeOrgCmd.Flags().Lookup("exclude-repo"))). Verified with golangci-lint run ./cmd/... and go test -v ./models in Docker.