xds: Add SNI related field in handshake info

[eshitachandwani]

This PR is part of A101 implementation.

This PR does the following changes:

1. Add sni and autoSniSanValidation field to handshake info.
2. Change the TLS config building to add SNI if env variable is true (currently false by default so will not be set), and sni is present (currently set as empty in handshake so will not be set).
3. Change verify function to match SANs against SNI if set and env variable and autoSniSanValidation is true (currently set to false by default).
4. Set sni to empty and autoSniSanValidation to false by default when creating handshake info in clusterimpl
5. Adds tests to verify the happy and failure cases of handshake.

In the next PR :

1. Will decide between hostname and SNI from CDS update in clusterimpl balancer.
2. Add end to end tests to verify the SNI flow.
3. Change the environment variable to true.

RELEASE NOTES: None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.34%. Comparing base (fd53961) to head (d42b8ab).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8965      +/-   ##
==========================================
+ Coverage   83.26%   83.34%   +0.08%     
==========================================
  Files         410      410              
  Lines       32576    32609      +33     
==========================================
+ Hits        27123    27178      +55     
+ Misses       4062     4050      -12     
+ Partials     1391     1381      -10     

Files with missing lines	Coverage Δ
internal/credentials/xds/handshake_info.go	93.71% <100.00%> (+0.46%)	⬆️
internal/xds/balancer/clusterimpl/clusterimpl.go	87.82% <100.00%> (ø)
internal/xds/server/conn_wrapper.go	76.27% <100.00%> (ø)

... and 31 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.