Adjust for data api client v2.2.1 GA

[sl-at-ibm]

Updates to the code to adjust to the GA client (v2.2.1).

• Naming aligment: DataApiClient => DataAPIClient
• .Update and .Filter aliased as .TableUpdate and .TableFilter (some features are/will be specializations; naming uniformity)
• removed PrimaryKeyFilter and CompositeKey from table filter builders (did not add anything other than cognitive load). Replaced with regular filtering syntax as required by latest client.
• README: removed 2 mentions of the package being beta
• likewise, bump dep version in kv-be-csharp-dataapi-table.csproj
• stronger nullchecks in a few controller logic (etc.) to avoid null deref build warnings.

Now it builds and runs, and...

$> curl -X GET "https://localhost:7264/api/v1/health" --header "Content-Type: application/json" --http1.0
curl: (56) OpenSSL SSL_read: OpenSSL/3.5.4: error:0A000126:SSL routines::unexpected eof while reading, errno 0
"Service is up and running!"
$>

(not sure about the SSL error, probably not a big deal/a me-problem, and surely unrelated to this PR)

Note I'd like to address the ~14 remaining build warnings (mostly related to null dereference risk and a few nullable things), but this can go in a separate PR.

[aar0np]

LGTM!