feat: add of offload threshold property in namespace configuration

[shodo]

Motivation

In the company I work with, we needed to enable "infinite" retention for certain topics. This paradigm requires offloading part of the topic to S3 when a certain size threshold is reached.
I know that Pulsar offers this configuration on a namespace level, but the Terraform plugin does not expose this configuration, so I'm creating this PR to add an offload_threshold_size_in_mb property to the namespace_config

Modifications

• Add of offload_threshold_size_in_mb property in the namespace_config
• Add a field in the related NamespaceConfig type
• Added code to parse the property and call the related pulsar client function

Verifying this change

• Make sure that the change passes the CI checks.

This change is already covered by existing tests, such as resource_pulsar_namespace_test.go, I've just added the new offload_threshold_size_in_mb in the testPulsarNamespace fixture.

Documentation

• [ x ] doc

[github-actions]

@shodo:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[github-actions]

@shodo:Thanks for providing doc info!

[maxsxu]

@shodo Thanks for contribution!

Could you update the docs by run go generate, since this PR introduced new param?

[ca-reviewer]

@shodo Thanks for contribution!

Could you update the docs by run go generate, since this PR introduced new param?

done!

[giacomo-porro]

Hi guys! I see this PR have been opened 5 months ago and I need the same functionality as @shodo implemented, is there any blocker to include the change in the next release? How can I help?

[shodo]

I've rebased my forked repo on the last changes and re-generated the doc to be 100% sure everything is aligned. Let me know if there is something I can do to speed up the merge

[maxsxu]

@shodo @giacomo-porro The terraform-provider-pulsar v0.3.1 has released and this PR included.

Thanks for your contributions again!