Add a charm config to add custom annotations to loadbalancers created by traefik #1151

Job	Run time
PR / Check against ignorelist	4s
Terraform / Terraform lint	3s
PR / Quality Checks / Check the CHARMHUB_TOKEN secret	1s
PR / Quality Checks / Inclusive naming / check	7s
PR / Quality Checks / Linting / Lint	17s
PR / Quality Checks / Static Analysis / Static Analysis of Libs	29s
PR / Quality Checks / Scenario Tests / Scenario tests	1m 18s
PR / Quality Checks / Unit Tests / Unit tests	35s
PR / Quality Checks / Static Analysis / Static Analysis of Charm	27s
PR / Quality Checks / Check libraries	37s
PR / Quality Checks / CodeQL analysis / Analyze (python)	1m 26s
PR / Quality Checks / Integration Tests / Integration Tests	5m 35s
	10m 59s

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