feat: add alias api with previousId support

[1abhishekpandey]

Description

• Added an Alias API with previousId support. Now, previousId can be passed and will be preferred over the existing userId or anonymousId.
• New Alias API:

public void alias(@NonNull String newId, @Nullable RudderOption option, @Nullable String previousId)

• This is to bring it in parity with the JS SDK so that previousId can be explicitly passed if needed.

NOTE: The change is backwards compatible, as we are introducing a new Alias API which adds a new behaviour to the existing payload schema.

How to test

Objective: We need to test, if previousId is passed then it should be used, else the existing behaviour should continue i.e., userId or anonymousId should be used.

• Make an alias event and explicitly pass previousId field -> It should be set as the previousId.
• Existing API: Make an Identify event, then RESET call and then an alias event (with previousId) -> previousId should be set as passed previousId.
• Existing API: Make an alias event with only newId -> previousId should be set as anonymousId.
• Existing API: Make an alias event with only newId and options -> previousId should be set as anonymousId.
• Existing API: Make an identify event and then an alias event (without previousId) -> previousId should be set as previous userId.
• Existing API: Make an Identify event, then RESET call and then an alias event (without previousId) -> previousId should be set as anonymousId.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• Version upgraded (project, README, gradle, podspec etc)
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added unit tests for the code
• I have made corresponding changes to the documentation

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud