fix(AboutModal): Add backgroung image to aboutModal

[mmelko]

This PR also adds possibility to set about background in the hawtconfig.json and adds RH backround that can be used in the the product.
closes #1031

Current about when running yarn start:

with the RH background-inverted:

[github-actions]

Test Results

  8 files  ±0    8 suites  ±0   57m 48s ⏱️ +22s
 66 tests ±0   64 ✅ ±0   2 💤 ±0  0 ❌ ±0 
536 runs  ±0  508 ✅ ±0  28 💤 ±0  0 ❌ ±0 

Results for commit 235b077. ± Comparison against base commit f0805fa.

[hawtio-ci]

Test results

Run attempt: 2599
Detailed summary

NAME	TESTS	PASSED ✅	SKIPPED 💤	FAILED ❌	ERRORS 🚫	TIME 🕖
test-results-quarkus-node(18)-java(17)-firefox	67	64	3	0	0	439.724
test-results-quarkus-node(18)-java(21)-firefox	67	64	3	0	0	428.853
test-results-quarkus-node(20)-java(17)-firefox	67	64	3	0	0	424.302
test-results-quarkus-node(20)-java(21)-firefox	67	64	3	0	0	437.632
test-results-springboot-node(18)-java(17)-firefox	67	63	4	0	0	427.057
test-results-springboot-node(18)-java(21)-firefox	67	63	4	0	0	445.997
test-results-springboot-node(20)-java(17)-firefox	67	63	4	0	0	425.909
test-results-springboot-node(20)-java(21)-firefox	67	63	4	0	0	439.174

[tadayosi]

please update hawtio-website once it's merged

https://hawt.io/docs/configuration.html#_hawtconfig_json