Adding pluggable secret store doc

[pravinpushkar]

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Description

Added Pluggable component secret store documentation.

Issue reference

closes #3783

[msfussell]

@pravinpushkar - Can you also add examples for implementing the .NET and Go components for the secret store, like these?

• https://docs.dapr.io/developing-applications/develop-components/pluggable-components/pluggable-components-sdks/pluggable-components-dotnet/
• https://docs.dapr.io/developing-applications/develop-components/pluggable-components/pluggable-components-sdks/pluggable-components-go/

Also if you check that this sample https://github.com/dapr/samples/tree/master/pluggable-components-dotnet-template still works for the v1.12 release and if so update the readme to say this is still valid for 1.12. That would be a huge bonus and benefit!! Thanks

[hhunter-ms]

lgtm

[msfussell]

@pravinpushkar - Can you look at my suggestions

[pravinpushkar]

@msfussell

@pravinpushkar - Can you also add examples for implementing the .NET and Go components for the secret store, like these?

• https://docs.dapr.io/developing-applications/develop-components/pluggable-components/pluggable-components-sdks/pluggable-components-dotnet/
• https://docs.dapr.io/developing-applications/develop-components/pluggable-components/pluggable-components-sdks/pluggable-components-go/

We cannot mention the developments usings SDKs yet. The .Net and Go PR for dapr-sandbox repo are under development and I will rebase the PRs as soon as stable runtime version 1.12 gets released. Once these PRs are merged, I can revisit this part of the doc.

Relevant PRs -

1. feat/secretstore dapr-sandbox/components-dotnet-sdk#42
2. [WIP]Local env secret store implementation dapr-sandbox/components-go-sdk#28

Also if you check that this sample https://github.com/dapr/samples/tree/master/pluggable-components-dotnet-template still works for the v1.12 release and if so update the readme to say this is still valid for 1.12. That would be a huge bonus and benefit!! Thanks

Samples works for 1.12. Just updated the Proto for state store and readme.md to be inline with latest enhancements.

Relevant PR - dapr/samples#164 (This is ready for review/merge)

[msfussell]

@pravinpushkar - Really appreciate getting the sample in. Will do the SDK updates later.
Thanks

[msfussell]

LGTM