Standardize README shield badges

[marcduiker]

We want to update the README for all Dapr repos so they all include shield badges for YouTube, Discord, X/Twitter and ensure they are all in the same style. See: https://github.com/dapr/community/issues/355

These are the shield badges for the java-sdk repo.

Snippet to include in the README:

 [![Maven Central](https://img.shields.io/maven-central/v/io.dapr/dapr-sdk.svg?label=Maven%20Central&style=flat)](https://central.sonatype.com/artifact/io.dapr/dapr-sdk) ![GitHub Actions Workflow Status](https://img.shields.io/github/actions/workflow/status/dapr/java-sdk/.github%2Fworkflows%2Fbuild.yml?branch=master&label=Build&logo=github) [![codecov](https://codecov.io/gh/dapr/java-sdk/branch/master/graph/badge.svg)](https://codecov.io/gh/dapr/java-sdk) ![GitHub License](https://img.shields.io/github/license/dapr/java-sdk?style=flat&label=License&logo=github) [![GitHub issue custom search in repo](https://img.shields.io/github/issues-search/dapr/java-sdk?query=type%3Aissue%20is%3Aopen%20label%3A%22good%20first%20issue%22&label=Good%20first%20issues&style=flat&logo=github)](https://github.com/dapr/java-sdk/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22) [![Discord](https://img.shields.io/discord/778680217417809931?label=Discord&style=flat&logo=discord)](http://bit.ly/dapr-discord) [![YouTube Channel Views](https://img.shields.io/youtube/channel/views/UCtpSQ9BLB_3EXdWAUQYwnRA?style=flat&label=YouTube%20views&logo=youtube)](https://youtube.com/@daprdev) [![X (formerly Twitter) Follow](https://img.shields.io/twitter/follow/daprdev?logo=x&style=flat)](https://twitter.com/daprdev)

Contributing

• Comment /assign on this issue if you want to self-assign this issue and update the README.
• Don't forget to sign off your commit, for more details see Developer Certificate of Origin (DCO) in the docs.

@ maintainers: Please label this as good first issue.