feat!(opentelemetry): migrate from opencensus to opentelemetry

[Sharponentielle]

What?

Flamingo uses Opencensus to collect application metrics and traces and transfer the data to a backend of the user's choice.
This pull request aims to replace Opencensus with Opentelemetry.

[Sharponentielle]

Since we want to guarantee backward compatibility with OpenCensus, I tried to use the OpenCensus bridge module. However, an open issue hinders me. I'm trying to find a workaround.

[Sharponentielle]

As of now, it's not possible to define boundaries for histograms at the instrument level with opentelemetry-go.
Issues: open-telemetry/opentelemetry-go#689, open-telemetry/opentelemetry-go#2678.

[github-actions]

Package	Line Rate	Health
flamingo.me/flamingo/v3/core/auth	10%	❌
flamingo.me/flamingo/v3/core/auth/fake	50%	➖
flamingo.me/flamingo/v3/core/auth/http	40%	❌
flamingo.me/flamingo/v3/core/auth/oauth	46%	❌
flamingo.me/flamingo/v3/core/cache	52%	➖
flamingo.me/flamingo/v3/core/gotemplate	87%	✔
flamingo.me/flamingo/v3/core/healthcheck/interfaces/controllers	76%	✔
flamingo.me/flamingo/v3/core/healthcheck	64%	➖
flamingo.me/flamingo/v3/core/internalauth/application	100%	✔
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/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/domain	62%	➖
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	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/interface/controller	100%	✔
flamingo.me/flamingo/v3/core/security/interface/middleware	72%	➖
flamingo.me/flamingo/v3/core/security	59%	➖
flamingo.me/flamingo/v3/core/zap	43%	❌
flamingo.me/flamingo/v3/framework/cmd	12%	❌
flamingo.me/flamingo/v3/framework/config	45%	❌
flamingo.me/flamingo/v3/framework/flamingo	8%	❌
flamingo.me/flamingo/v3/framework	28%	❌
flamingo.me/flamingo/v3/framework/opencensus	88%	✔
flamingo.me/flamingo/v3/framework/prefixrouter	44%	❌
flamingo.me/flamingo/v3/framework/systemendpoint	27%	❌
flamingo.me/flamingo/v3/framework/testutil	0%	❌
flamingo.me/flamingo/v3/framework/web	49%	❌
Summary	48% (3132 / 6551)	❌

[karstenkoehler]

• rebase onto latest version of master
• upgrade all otel packages to latest version
• check if all traces have been migrated to otel
• check if all metrics have been migrated to otel
• test if opencensus module still works as before
• check if new opentelemetry module works as expected
• [optional] move new opentelemetry module to separate repository

[karstenkoehler]

OpenTelemetry module now has its own repository: https://github.com/i-love-flamingo/opentelemetry

We can not merge this PR right now, because it contains breaking changes. With all the traces and metrics moved to the OpenTelemetry API, they are no longer exposed for the opencensus module. So we have to keep this PR around, until we decide to go for a flamingo v4 that accepts breaking changes.

I created another PR to mark the opencensus module as deprecated, see #364