Ability to set branch rules on a SourceRepository

## Describe your feature request

Ability to set branch rules on a SourceRepository.

## Describe the solution you'd like

A new `branchRules` property in the SourceRepository constructor allowing a user to control branch rules.

## Describe alternatives you've considered

N/A.

## Additional context

N/A.

Locate the TypeScript definition and constructor for SourceRepository. Read how existing constructor properties are represented and check whether branch-rule behavior or tests are documented elsewhere. Done means users can provide a branchRules property and it controls branch rules as requested, but the issue does not specify the supported rule shape or validation.

Written by the indexing model from the issue text.