This pull request adds the configuration and CI steps to build and
publish a container wrapping the `dendrite-demo-pinecone` command as
well as fixes a sentence structure issue in the pull request template.
As this does not touch any go source code no tests have been added
### Pull Request Checklist
<!-- Please read docs/CONTRIBUTING.md before submitting your pull
request -->
* [x] I have added tests for PR _or_ I have justified why this PR
doesn't need tests.
* [x] Pull request includes a [sign
off](https://github.com/matrix-org/dendrite/blob/main/docs/CONTRIBUTING.md#sign-off)
Signed-off-by: networkException <git@nwex.de> (by private sign-off)
Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
