Fix UserAgent encoding

[FabianMeiswinkel]

Description

When customers use special characters (outside ASCII 0 - 127) in the user agent suffix attempts to connect to the service are blocked when the account is moved to ComputeGateway (it still works when the account is on Routing Gateway). The UserAgent is passed as an http header - and the HTTP spec has in the meantime updated to only allow ASCII characters for http headers (it was initially kept more vague/open - allowing ISO-8859-1) - but then later was narrowed down to ASCII based on the fact that the vast majority of HTTP stacks in the wild only supported ASCII anyway.

This PR masks all non-ASCII characters in UserAgent - by using its matching ASCII character if possible or replacing any remaining non-ASCII character with '_'

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[FabianMeiswinkel]

/azp run java - cosmos - spark

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[FabianMeiswinkel]

/azp run java - cosmos - tests

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[xinlian12]

LGTM, thanks

[FabianMeiswinkel]

Test failures remaining are known flaky tests.

[FabianMeiswinkel]

/check-enforcer override