docs: Correct the agent documentation to reflect "name" field now being required.

[JonathanBerkeley]

Issue #, if available: https://github.com/aws/amazon-q-developer-cli/issues/3231

Description of changes: The "name" field for an agent has become mandatory since this commit: https://github.com/aws/amazon-q-developer-cli/commit/dc0974fad9c5da624c77311d536069f082698a94#diff-61df6179f46d679df0c7da318067babd72d265d8958e1b94e3a990de0bfba45fL123-L124

The "/agent generate" command also requires providing a name: https://github.com/aws/amazon-q-developer-cli/commit/a8afb479f8cbb9390e28560ccc198943316ad2c1#diff-f6d402f6ca61a5601d188759a5d5246ceb57016fa6744f5bbbdec85180ff7a2cR1606

This commit is to update the docs to match current functionality, and fix non-working example snippets which omit the "name" field.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[JonathanBerkeley]

Hi @dingfeli, could this get a review? I created this to fix a minor documentation issue that I noticed after Amazon Q used the "introspect" tool and produced an invalid agent specification due to it.

Sorry if pinging is improper etiquette for this repo!

[JonathanBerkeley]

Hello @brandonskiser, could I get a review for this? Thanks.