Introduce additional metadata field to Context

[mpanchajanya]

What this PR does / why we need it

• At the moment, Tanzu Plugin Runtime - Context configuration does not provide a means to add any additional metadata.
  This proposal introduces a new AdditionalMetadata map field to Context to be able to provide additional data for each context. This way we don't have to release a new version of runtime every time we add a new property to the context object.
  Example: TMC will need to store a few additional properties for each context and the fields could change in future. In TMC Self-Managed with VCD's login flow, it requires "VCD org" and "VCD OIDC client ID" to be persisted in context, so that TMC Plugins can auto-refresh or re-trigger the token flow if needed when a TMC plugin command is called.

Example usage:

• Add two new properties to context

ctx := &Context {
 Name: tanzu-ctx,
 AdditionalMetadata : map[string]interface{
  “token” : “test-token”
  “issuer” : “test-issuer”
 }
}
SetContext(ctx)  // ctx will  now have both token and issuer metadata

• Update the existing additional metadata of a context

# To merge the additional metadata

ctx := GetContext()
ctx.AdditionalMetadata[“token”]=”updated-token”
SetContext(ctx)  // ctx will now have both issuer and token metadata


# To replace the additional metadata

ctx := GetContext()
ctx.AdditionalMetadata := map[string]interface{}{
 “token”=”only-token”,
}
SetContext(ctx) // Ctx will only have token metadata

# To delete the entire additional metadata

ctx := GetContext()
ctx.AdditionalMetadata := map[string]interface{}{}
SetContext(ctx) // Ctx will not have any additional metadata

Which issue(s) this PR fixes

Fixes #

Describe testing done for PR

Added unit tests and integrated tests

Release note

 Introduce new additionalMetadata field in Context

Additional information

Special notes for your reviewer

[anujc25]

LGTM. Thanks