xds: return all ServerConfig dial options together

[eshitachandwani]

Fixes : #7661

• Added a single DialOptions() method that returns a slice of all dial options for the type ServerConfig instead of individual methods to get all dial options.
• Removed the TestNewWithDialerFromCredentialsBundle test since it was already being tested here in TestClientCustomDialerFromCredentialsBundle (b8ee37d/test/xds/xds_client_custom_dialer_test.go#L83C10-L83C53)

RELEASE NOTES: None

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.85%. Comparing base (b8ee37d) to head (fa8d5c1).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7718      +/-   ##
==========================================
+ Coverage   81.84%   81.85%   +0.01%     
==========================================
  Files         361      361              
  Lines       27827    27825       -2     
==========================================
+ Hits        22775    22777       +2     
- Misses       3850     3852       +2     
+ Partials     1202     1196       -6     

Files with missing lines	Coverage Δ
internal/xds/bootstrap/bootstrap.go	71.56% <100.00%> (+0.08%)	⬆️
xds/internal/xdsclient/transport/transport.go	92.43% <100.00%> (-0.88%)	⬇️

... and 18 files with indirect coverage changes