[#1651] improvement(netty): Set Netty as the default server type

[rickyma]

What changes were proposed in this pull request?

1. Set Netty as the default server type.
2. Update related docs.
3. Change the default values of configurations rss.server.buffer.capacity.ratio and rss.server.read.buffer.capacity.ratio.
4. Fix UTs. Some UTs have bugs when testing Netty.

Why are the changes needed?

For #1651.

Also, change the default values of configurations rss.server.buffer.capacity.ratio and rss.server.read.buffer.capacity.ratio, which are more sensible. Because in our tests, we discovered that the metric read_used_buffer_size could potentially only reach up to 3.75GB. The configuration for the shuffle server is: capacity: 140GB, readCapacity: 20GB, and it's under high pressure and high concurrency situations. So I think the default value for rss.server.read.buffer.capacity.ratio is a little bit too high. We can decrease the default value of rss.server.read.buffer.capacity.ratio and increase the default value of rss.server.buffer.capacity.ratio.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Updated UTs.

[github-actions]

Test Results

 2 384 files  ±0   2 384 suites  ±0   4h 39m 27s ⏱️ + 6m 59s
   919 tests ±0     918 ✅ ±0   1 💤 ±0  0 ❌ ±0 
10 666 runs  ±0  10 652 ✅ ±0  14 💤 ±0  0 ❌ ±0 

Results for commit 545ad8c. ± Comparison against base commit 5ab625b.

♻️ This comment has been updated with latest results.

[rickyma]

@zuston @jerqi PTAL.

[zuston]

I concern 2 points.

1. This is a big change for users, and the upgrade is not compatible with version < 0.8 .
2. Netty will be set as the default only after it can be used on a large scale online.

[rickyma]

We will put the Netty version of Uniffle in production this month. If you are concerned, we can hold off on this PR for now.