feat: decouple opencensus from core

[tessig]

This is in preparation of the opentelemetry drop-in replacement

[github-actions]

Package	Line Rate	Health
flamingo.me/flamingo/v3	0%	❌
flamingo.me/flamingo/v3/core/auth	13%	❌
flamingo.me/flamingo/v3/core/auth/example/custom	0%	❌
flamingo.me/flamingo/v3/core/auth/example	0%	❌
flamingo.me/flamingo/v3/core/auth/fake	50%	➖
flamingo.me/flamingo/v3/core/auth/http	40%	❌
flamingo.me/flamingo/v3/core/auth/mock	0%	❌
flamingo.me/flamingo/v3/core/auth/oauth	49%	❌
flamingo.me/flamingo/v3/core/cache	66%	➖
flamingo.me/flamingo/v3/core/gotemplate	87%	✔
flamingo.me/flamingo/v3/core/healthcheck/domain/healthcheck	0%	❌
flamingo.me/flamingo/v3/core/healthcheck/interfaces/controllers	76%	✔
flamingo.me/flamingo/v3/core/healthcheck	66%	➖
flamingo.me/flamingo/v3/core/internalauth/application	88%	✔
flamingo.me/flamingo/v3/core/internalauth	100%	✔
flamingo.me/flamingo/v3/core/locale/application	87%	✔
flamingo.me/flamingo/v3/core/locale/domain	75%	✔
flamingo.me/flamingo/v3/core/locale/infrastructure/fake	75%	✔
flamingo.me/flamingo/v3/core/locale/infrastructure	0%	❌
flamingo.me/flamingo/v3/core/locale/interfaces/controllers	100%	✔
flamingo.me/flamingo/v3/core/locale/interfaces/templatefunctions	92%	✔
flamingo.me/flamingo/v3/core/locale	59%	➖
flamingo.me/flamingo/v3/core/oauth/application	4%	❌
flamingo.me/flamingo/v3/core/oauth/application/fake	50%	➖
flamingo.me/flamingo/v3/core/oauth/domain	62%	➖
flamingo.me/flamingo/v3/core/oauth/example	0%	❌
flamingo.me/flamingo/v3/core/oauth/infrastructure	0%	❌
flamingo.me/flamingo/v3/core/oauth/interfaces	1%	❌
flamingo.me/flamingo/v3/core/oauth/interfaces/fake	0%	❌
flamingo.me/flamingo/v3/core/oauth	55%	➖
flamingo.me/flamingo/v3/core/requestlogger	100%	✔
flamingo.me/flamingo/v3/core/requesttask	10%	❌
flamingo.me/flamingo/v3/core/robotstxt/interfaces	0%	❌
flamingo.me/flamingo/v3/core/robotstxt	50%	➖
flamingo.me/flamingo/v3/core/runtime	77%	✔
flamingo.me/flamingo/v3/core/security/application/role	95%	✔
flamingo.me/flamingo/v3/core/security/application	98%	✔
flamingo.me/flamingo/v3/core/security/application/voter	100%	✔
flamingo.me/flamingo/v3/core/security/domain	17%	❌
flamingo.me/flamingo/v3/core/security/interface/controller	100%	✔
flamingo.me/flamingo/v3/core/security/interface/middleware	72%	➖
flamingo.me/flamingo/v3/core/security	59%	➖
flamingo.me/flamingo/v3/core/silentzap	0%	❌
flamingo.me/flamingo/v3/core/zap	78%	✔
flamingo.me/flamingo/v3/examples/hello-world	0%	❌
flamingo.me/flamingo/v3/framework/cmd	12%	❌
flamingo.me/flamingo/v3/framework/config	49%	❌
flamingo.me/flamingo/v3/framework/controller	0%	❌
flamingo.me/flamingo/v3/framework/flamingo	37%	❌
flamingo.me/flamingo/v3/framework/flamingo/healthcheck	0%	❌
flamingo.me/flamingo/v3/framework	28%	❌
flamingo.me/flamingo/v3/framework/opencensus	78%	✔
flamingo.me/flamingo/v3/framework/prefixrouter	46%	❌
flamingo.me/flamingo/v3/framework/systemendpoint/application	0%	❌
flamingo.me/flamingo/v3/framework/systemendpoint	27%	❌
flamingo.me/flamingo/v3/framework/testutil	0%	❌
flamingo.me/flamingo/v3/framework/web	48%	❌
flamingo.me/flamingo/v3/framework/web/filter	2%	❌
Summary	42% (3539 / 8477)	❌

[carstendietrich]

LGTM