Service level overview front matter order should be deterministic

Right now service level overview generation can result in noisy PRs with no useful changes because PowerShell does not guarantee order of traversal of hash table keys.

The result is noisy PRs like this one: https://github.com/MicrosoftDocs/azure-docs-sdk-python/pull/1604/files#diff-a61e87c33fdd7ba47af360fd0280c395aad5eab3829d00599f13fb2128f60969 where the changes to the file aren't useful.

To fix, [I think we need an `[ordered]@{ ... }` hash when generating `$metadataTable`](https://github.com/Azure/azure-sdk-for-python/blob/main/eng/common/scripts/Helpers/Metadata-Helpers.ps1#L133). That may be sufficient, if not, we should also alphebatize the keys here: https://github.com/Azure/azure-sdk-for-python/blob/main/eng/common/scripts/Helpers/Metadata-Helpers.ps1#L97 ... we should probably also [alphabetize the keys coming back from `ConvertFrom-StringData`](https://github.com/Azure/azure-sdk-for-python/blob/main/eng/common/scripts/Helpers/Metadata-Helpers.ps1#L102)