Add OpenSSL to dev environment

[supersven]

The openssl binary is required by deploy/services-demo/demo.sh.

I've noticed this while getting following error:

➜  wire-server git:(pcapriotti/cargohold-servant) ✗ ./deploy/services-demo/demo.sh 
Generate a secret for the TURN servers (must match the turn.secret key in brig's config)...
./deploy/services-demo/demo.sh: Zeile 61: openssl: Kommando nicht gefunden.

Zeile 61: openssl: Kommando nicht gefunden. translates to Line 61: openssl: Command not found

Checklist

• [X] The PR Title explains the impact of the change.
• [X] The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• [ ] If HTTP endpoint paths have been added or renamed, the endpoint / config-flag checklist (see Wire-employee only backend wiki page) has been followed.
• [ ] If a cassandra schema migration has been added, I ran make git-add-cassandra-schema to update the cassandra schema documentation.
• [ ] changelog.d contains the following bits of information (details):
  • [ ] A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.
  • [ ] If new config options introduced: added usage description under docs/reference/config-options.md
  • [ ] If new config options introduced: recommended measures to be taken by on-premise instance operators.
  • [ ] If a cassandra schema migration is backwards incompatible (see also these docs), measures to be taken by on-premise instance operators are explained.
  • [ ] If a data migration (not schema migration) introduced: measures to be taken by on-premise instance operators.
  • [ ] If public end-points have been changed or added: does nginz need un upgrade?
  • [ ] If internal end-points have been added or changed: which services have to be deployed in a specific order?

[supersven]

Converted to draft because I'm currently experiencing issues in my dev env and would like to make sure this PR isn't related.

[CLAassistant]

All committers have signed the CLA.

[julialongtin]

do we still need this?