Decouple the Target association with the Context object by introducing ContextType

[anujc25]

What this PR does / why we need it

Background:

• Today, Tanzu CLI does not have a concept of Context-Type and we use the same concept Target to represent different types of Context as well as how we group plugins under the Tanzu CLI command tree.
• In the existing Tanzu CLI code implementation, a single custom datatype Target is used to represent both the Context-Type and Target concept making both concepts tightly coupled.
• Today, Target also has some values like global which does not make sense as a Context-Type value and the code assumes that value cannot be a value of a Context-Type.
• Because of the above, Creating a new Target has the effect of representing a new type of context and groups a set of plugins, but sometimes one of the consequences is unintended.

Change:

• As part of this PR we are introducing a new field called ContextType within the Context object and Deprecating the existing Target field.
• The Target field will be kept and set correctly to support CLI and plugins using the previous version of Tanzu Plugin Runtime.

Which issue(s) this PR fixes

Fixes #116

Describe testing done for PR

• Added/Updated Unit tests
• Added/Updated Compatibility tests

Test Cases that I am trying to cover:

Unit Test Cases:

1. Set Context with Target only, Get the Context and it should contain Target and ContextType both
2. Set Context with ContextType Only, Get the Context and it should contain Target and ContextType both
3. Set Context with Target:X and ContextType:Y, It should throw validation error while setting.

Compatibility Test Cases:

1. Set the Context with v1.1.0 CLI (with setting only ContextType) , Get the Context with previous version of CLIs and it should contain correct Target
2. Set the Context with v1.1.0 CLI (with setting only Target), Get the Context with previous version of CLIs and it should contain correct Target
3. Set the Context with v0.90 CLI (with Target),
4. Get the Context with v0.28, v0.90 version of CLI should return context with correct Target
5. Get the Context with v1.1.0 version of CLI should return context with correct Target and ContextType

Release note

Decouple the Target association with the Context object by introducing ContextType

The following APIs are marked as Deprecated:
- `SetCurrentContext` is deprecated. Use `SetActiveContext` instead
- `GetCurrentContext` is deprecated. Use `GetActiveContext` instead
- `RemoveCurrentContext` is deprecated. Use `RemoveActiveContext` instead
- `GetAllCurrentContextsMap` is deprecated. Use `GetAllActiveContextsMap` instead
- `GetAllCurrentContextsList` is deprecated. Use `GetAllActiveContextsList` instead
- `SyncPluginsForTarget` is deprecated. Use `SyncPluginsForContextType` instead

API Change:
- The `ClientConfig` API contains a notable datatype change of the `CurrentContext` field from `map[Target]string` to `map[ContextType]string`.
- If you are using the `CurrentContext` directly by processing the entire `ClientConfig` object some change might be required. However, we encourage teams to use fine-grained API `GetActiveContext` to get active context.

Additional information

Special notes for your reviewer

[marckhouzam]

Is it possible to remove the constants TargetTAE and targetTAE since they are not in any official release? Looking at the code, I realize this will complicate things. However, I think it is important so that we make sure we adapt the code to handle having different contextTypes than Targets; that way, if we need to add another new contextType, we will be ready and not need to also add it as a new target. But this implies completely removing the use of context.Target in the code.

The above will probably complicate this PR a lot. Given the time frame, we should discuss doing it in two phases:

1. continue as you did by introducing contextType but continuing to use Target by making sure the two are in sync
2. and after, remove all uses of context.Target.

[vuil]

Nit: perhaps for consistency, in test cases (e.g. clientconfig_test/context_additionalmetadata_test/context_test) where the use of the Target: field is not consequential, we should be consistent and update them to specify the equivalent ContextType instead.

[marckhouzam]

A couple of nits on the latest version

[anujc25]

Rebased the PR on top of 6cabd02 commit.

[vuil]

LGTM, thanks for the changes and revisions as well.

[vuil]

We can probably use a little more documentation (here or in TZC) to clarify the Context Type introduction.

[anujc25]

We can probably use a little more documentation (here or in TZC) to clarify the Context Type introduction.

Yes agreed. I will be adding more documentation around the Context Type as part of the follow-up PR.