[CI] Improvements to Solr image publishing

[mnocon]

Follow-up with the suggestions made in #303

1. First commit is the file rename - no other changes
2. Second commit adds:

• cron schedule (run once every month)
• image testing - Solr integration tests are run after the image is built and tagged. The image will be pushed if one of the conditions is met:
  a) if the tests are successful
  b) if the force input has been checked in manual dispatch

I've run some tests, here is the summary: (things to look at: test result and the Debug step):

1. Standard build (cron): https://github.com/ibexa/core/actions/runs/7186371453/job/19571619912?pr=304 . Does not publish the image on test fail.
2. Manual build without the force flag: https://github.com/ibexa/core/actions/runs/7186411004 Does not publish the image on test fail.
3. Manual build with force flag: https://github.com/ibexa/core/actions/runs/7186412982 Publishes new image on test fail.
4. Build with the tests passing (https://github.com/ibexa/core/actions/runs/7186467402/job/19571912873?pr=304)

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
2.4% Duplication on New Code

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
1.1% Duplication on New Code

See analysis details on SonarCloud