Add support for third-party services

[cmeessen]

Fixes #1288

Changes proposed in this pull request:

• adds support for third-party services via plugin slots in the user interface. The plugin slots are links that are provided by third-party services
• supports an arbitrary amount of plugins
• currently implemented slots are: userMenu and softwareEditNav (see type PluginSlot)
• adds a documentation
• adds syntax highlighting in docusaurus for json, nginx and typescript
• adds a data attribute to the user token which contains eduPersonEntitlements if the user logs in via HelmholtzID

How to test:

• follow steps to setup example plugin container in research-software-directory/RSD-plugin-example (in progress)
• login
• verify that plugin slots are shown including svg icons in the user menu and in the software edit navigation sidebar

PR Checklist:

• [ ] Increase version numbers in docker-compose.yml
• [x] Link to a GitHub issue
• [x] Update documentation
• [ ] Tests

[sonarcloud[bot]]

Quality Gate passed for 'authentication'

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
5.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarcloud[bot]]

Quality Gate failed for 'rsd-frontend'

Failed conditions
1 Security Hotspot

See analysis details on SonarCloud

[cmeessen]

Sonar cloud complains about http being insecure. This is not relevant here, because the communication happens inside the docker network.