`azuredevops_build_definition ` - Change `name` from optional to required

[xuzhang3]

All Submissions:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [x] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.
• [x] My code follows the code style of this project.
• [x] I ran lint checks locally prior to submission.
• [x] Have you checked to ensure there aren't other open PRs for the same update/change?

What about the current behavior has changed?

Issue Number: #1122

=== RUN   TestAccBuildDefinition_DataSource
=== PAUSE TestAccBuildDefinition_DataSource
=== RUN   TestAccBuildDefinition_with_path_DataSource
=== PAUSE TestAccBuildDefinition_with_path_DataSource
=== RUN   TestAccBuildDefinition_Basic
=== PAUSE TestAccBuildDefinition_Basic
=== RUN   TestAccBuildDefinition_PathUpdate
=== PAUSE TestAccBuildDefinition_PathUpdate
=== RUN   TestAccBuildDefinition_WithVariables
=== PAUSE TestAccBuildDefinition_WithVariables
=== RUN   TestAccBuildDefinition_Schedules
=== PAUSE TestAccBuildDefinition_Schedules
=== CONT  TestAccBuildDefinition_DataSource
=== CONT  TestAccBuildDefinition_PathUpdate
=== CONT  TestAccBuildDefinition_Basic
=== CONT  TestAccBuildDefinition_with_path_DataSource
=== CONT  TestAccBuildDefinition_Schedules
=== CONT  TestAccBuildDefinition_WithVariables
--- PASS: TestAccBuildDefinition_with_path_DataSource (57.93s)
--- PASS: TestAccBuildDefinition_DataSource (64.17s)
--- PASS: TestAccBuildDefinition_PathUpdate (79.07s)
--- PASS: TestAccBuildDefinition_WithVariables (98.56s)
--- PASS: TestAccBuildDefinition_Basic (123.98s)
--- PASS: TestAccBuildDefinition_Schedules (128.34s)
PASS
ok      github.com/microsoft/terraform-provider-azuredevops/azuredevops/internal/acceptancetests        130.191s

Does this introduce a change to go.mod, go.sum or vendor/?

• [ ] Yes
• [x] No

Does this introduce a breaking change?

• [ ] Yes
• [x] No

Any relevant logs, error output, etc?

(If it’s long, please paste to https://ghostbin.com/ and insert the link here.)

Other information