(tree) Tag incremental summary APIs as @alpha

[agarwal-navin]

The APIs neede to enable incremental summary have been tagged as @ alpha so that they can be used by applications.
The list of APIs that are marked @ alpha:

• configuredSharedTreeAlpha - This is a new API which is similar to configuredSharedTreeBeta but has a couple more options exposed for configuring incremental summaries.
• SharedTreeOptionsAlpha - Extension of SharedTreeOptionsBeta that includes options to enable incremental summarization.
• IncrementalEncodingPolicy - Policy type to determine whether a node / field should be incrementally encoded.
• incrementalEncodingPolicyForAllowedTypes - This function returns an IncrementalEncodingPolicy which will determine if AllowedTypes are opted into incremental summarization.
• incrementalSummaryHint - This is a symbol that should be put in the metadata property of AllowedTypes to opt-in these types to be incrementally summarized.

AB#54252
AB#46028

[noencke]

I don't think this should be a Partial. If SharedTreeOptionsPublic or Beta or Alpha has a required parameter, then SharedTreeOptionsInternal needs to supply that as well to be compatible.

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> fluid-framework-docs-site@0.0.0 ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> fluid-framework-docs-site@0.0.0 serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> fluid-framework-docs-site@0.0.0 check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  249533 links
    1776 destination URLs
    2013 URLs ignored
       0 warnings
       0 errors