return empty dataframe on create table, remove a duplicate optimize call

[kmitchener]

update docs

Which issue does this PR close?

Closes #3265 .

Rationale for this change

What changes are included in this PR?

• per issue, successful create table returns an empty dataframe instead of a full select of what's in the table
• removed an extra optimize() call during creation
• updated docs

Are there any user-facing changes?

Slight. When creating a table in datafusion-cli, it will no longer return the contents of the table created.

[andygrove]

LGTM. Thanks @kmitchener

[Dandandan]

Thanks @kmitchener

[ursabot]

Benchmark runs are scheduled for baseline = 4c948a3 and contender = ede82fb. ede82fb is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java