prepare release 2.8.0

[liubao68]

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a JIRA issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a JIRA issue. Your pull request should address just this issue, without pulling in other changes.
• Each commit in the pull request should have a meaningful subject line and body.
• Format the pull request title like [SCB-XXX] Fixes bug in ApproximateQuantiles, where you replace SCB-XXX with the appropriate JIRA issue.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Run mvn clean install -Pit to make sure basic checks pass. A more thorough check will be performed on your pull request automatically.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

---

[codecov-commenter]

Codecov Report

Merging #3369 (484030e) into master (02c3837) will increase coverage by 0.00%.
The diff coverage is 75.00%.

@@            Coverage Diff            @@
##             master    #3369   +/-   ##
=========================================
  Coverage     77.56%   77.57%           
  Complexity     1463     1463           
=========================================
  Files          1650     1650           
  Lines         43806    43799    -7     
  Branches       3687     3685    -2     
=========================================
- Hits          33977    33975    -2     
+ Misses         8289     8288    -1     
+ Partials       1540     1536    -4     

Impacted Files	Coverage Δ
...java/org/apache/servicecomb/it/deploy/Deploys.java	74.46% <75.00%> (+0.81%)	⬆️
.../servicecomb/registry/discovery/DiscoveryTree.java	96.49% <0.00%> (-3.51%)	⬇️
...egistry/client/http/ServiceRegistryClientImpl.java	71.31% <0.00%> (+0.38%)	⬆️
...thentication/consumer/RSAConsumerTokenManager.java	77.41% <0.00%> (+6.45%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more