Add missing fields in config.md docs

[PuneetPunamiya]

Feature request

Currently there are some fields which might be supported as per the code base,
but are not included in the config.md docs

Fields from config.go such as

ociRepositoryInsecureKey   = "storage.oci.repository.insecure"
pubsubProvider             = "storage.pubsub.provider"
pubsubTopic                = "storage.pubsub.topic"
pubsubKafkaBootstrapServer = "storage.pubsub.kafka.bootstrap.servers"

are the fields which are not documented yet in config.md docs

[lcarva]

storage.oci.repository.insecure is honored when uploading payloads to an OCI repository. This allows signatures and attestations to be pushed to an OCI registry without TLS. The value should be either "true" or "false".

storage.pubsub.provider used to configure how payloads are stored with pub sub. Possible values are "inmemory" or "kafka".

storage.pubsub.topic configures the pub sub topic to be used. The value should be a valid topic for the configured storage.pubsub.provider.

pubsubKafkaBootstrapServers holds the kafka server address to be used. NOTE: It looks like this currently only allows a single server value, even though the config key is in the plural form. This may have been an oversight. Adding support to multiple looks trivial.

The pubsub storage is marked as experimental which may be why it's not listed in config.md. pubsub is not mentioned at all there. It is mentioned in experimental.md. So maybe the config options should be documented there instead?

Looking at the code, I don't really see how someone could even enable pubsub today. For example, artifacts.taskrun.storage could be set to "kafka". However, InitializeBackends looks for the "pubsub" value (which the config doesn't accept!). So it looks like this experimental feature is likely abandoned.

Maybe @wlynch has more insight into this?

[tekton-robot]

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[lcarva]

/lifecycle frozen

we should do this.