Add participant self-description

[bscholtes1A]

What this PR changes/adds

Generate a Gaia-X Self-Description based on a template for each participant and inject it into the associated Identity Hub.

Why it does that

Self-Description of each participant should be exposed.

Linked Issue(s)

186

Checklist

• [ ] added appropriate tests?
• [ ] performed checkstyle check locally?
• [ ] added/updated copyright headers?
• [ ] documented public classes/methods?
• [ ] added/updated relevant documentation?
• [ ] added relevant details to the changelog? (skip with label no-changelog)
• [ ] formatted title correctly?

[github-actions[bot]]

Unit Test Results

  7 files  ±0    7 suites  ±0   46s :stopwatch: +5s 27 tests ±0  26 :heavy_check_mark: ±0  1 :zzz: ±0  0 :x: ±0  30 runs  +3  29 :heavy_check_mark: +3  1 :zzz: ±0  0 :x: ±0 

Results for commit 23e61a0a. ± Comparison against base commit 8e1c8802.

This pull request removes 3 and adds 3 tests. Note that renamed tests count towards both.

``` org.eclipse.dataspaceconnector.system.tests.identityhub.IdentityHubIntegrationTest ‑ [1] http://localhost:8181/api/identity-hub, eu org.eclipse.dataspaceconnector.system.tests.identityhub.IdentityHubIntegrationTest ‑ [2] http://localhost:8182/api/identity-hub, eu org.eclipse.dataspaceconnector.system.tests.identityhub.IdentityHubIntegrationTest ‑ [3] http://localhost:8183/api/identity-hub, us ``` ``` org.eclipse.dataspaceconnector.system.tests.identityhub.IdentityHubIntegrationTest ‑ [1] http://localhost:8181/api/identity-hub, eu, FR org.eclipse.dataspaceconnector.system.tests.identityhub.IdentityHubIntegrationTest ‑ [2] http://localhost:8182/api/identity-hub, eu, DE org.eclipse.dataspaceconnector.system.tests.identityhub.IdentityHubIntegrationTest ‑ [3] http://localhost:8183/api/identity-hub, us, US ```

:recycle: This comment has been updated with latest results.