Bump to 2.0.0-preview5

What's Changed

• [release] 2.0.0.preview.4 by @corinagum in #248
• Fix add text-flag for at-mention by @heyitsaamir in #249
• [devtools] Update Chat rendering to support blockquote by @Jesperholmbergmsft in #254
• [apps] fix streaming retry logic by @aacebo in #256

Full Changelog: https://github.com/microsoft/teams.ts/compare/@microsoft/[email protected]...@microsoft/[email protected]