fix(client): don't throw IndexOutOfBounds exceptions when calling write with null reads and writes

[jimmyjames]

Description

Don't fail with an IndexOutOfBounds exceptions when calling write with null reads and writes.

• from java-sdk calling the server without content when submitting empty deletes and writes sdk-generator#307

Also includes some chores (all in separate commits):

• improved issue templates. From chore: improve issue templates for the generator and the SDKs sdk-generator#315
• use slack instead of discord. From chore: use slack instead of discord sdk-generator#318
• read API docs updated. From docs: update Read description api#133
• document that only one OpenFgaClient should be created and used. From chore(docs): add note about initializing the OpenFgaClient only once sdk-generator#312

References

• java-sdk calling the server without content when submitting empty deletes and writes sdk-generator#307
• chore: improve issue templates for the generator and the SDKs sdk-generator#315
• chore: use slack instead of discord sdk-generator#318
• docs: update Read description api#133
• chore(docs): add note about initializing the OpenFgaClient only once sdk-generator#312

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected