feat: Add organization migration options

[leo-belanger]

Implements #3597

Add support for two options of the migrate organization endpoint:

• ExcludeReleases
• Exclude

Here are a couple of manual test scenarios

Exclude repositories from response

func Test_ExcludeRepositories(t *testing.T) {
client := github.NewClient(nil).WithAuthToken("GITHUB_AUTH_TOKEN")
m, _, err := client.Migrations.StartMigration(context.Background(), "GITHUB_ORG", []string{"GITHUB_ORG_REPO"}, &github.MigrationOptions{
Exclude: []string{"repositories"},
})
assert.NoError(t, err)
assert.Empty(t, m.Repositories)
}

Exclude releases from response

func Test_ExcludeReleases(t *testing.T) {
client := github.NewClient(nil).WithAuthToken("GITHUB_AUTH_TOKEN")
m, _, err := client.Migrations.StartMigration(context.Background(), "GITHUB_ORG", []string{"GITHUB_ORG_REPO"}, &github.MigrationOptions{
ExcludeReleases: true,
})
assert.NoError(t, err)
url, err := client.Migrations.MigrationArchiveURL(context.Background(), "GITHUB_ORG", m.GetID())
assert.NoError(t, err)
fmt.Println(url)
// Then download the tarball and confirm that the releases were not migrated
// There sould be no `releases_*.json` file
}

Without new options (regression testing)

func Test_Regression(t *testing.T) {
client := github.NewClient(nil).WithAuthToken("GITHUB_AUTH_TOKEN")
_, _, err := client.Migrations.StartMigration(context.Background(), "GITHUB_ORG", []string{"GITHUB_ORG_REPO"}, &github.MigrationOptions{})
assert.NoError(t, err)
} 

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[gmlewis]

Please run step 4 of CONTRIBUTING.md and push the changes to this PR.
Thank you, @leo-belanger!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.32%. Comparing base (ad671c4) to head (b8d629e).
Report is 8 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3606 +/- ##
=======================================
Coverage 91.32% 91.32% =======================================
Files 184 184 Lines 16143 16148 +5 =======================================
+ Hits 14742 14747 +5 
Misses 1227 1227 Partials 174 174 

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[leo-belanger]

Please run step 4 of CONTRIBUTING.md and push the changes to this PR. Thank you, @leo-belanger!

@gmlewis Already done :)

[gmlewis]

Thank you, @leo-belanger!
LGTM.
Merging.