credentials/tls: Splitting host and port of `authority` header

[Atul1710]

Fixes: https://github.com/grpc/grpc-go/issues/8719

Splits the host and port in the HTTP2 :authority header in ValidateAuthority before calling VerifyHostname. Added test cases to check multiple different types of values possible for :authority

RELEASE NOTES:

• tls: strip port before validating authority override.

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: Atul1710 / name: Atul Suresh Kumar (417442b65766dde74c83f971a952f558446fec4a, 7baceed18b3c6067fb81b25e63a9509a5905c26f, aa986e201a95ee57abd21c9a9e56008da7da396f, bf90c39772616230f55f5d29dca9be528f9f8959, cf93c27b3f9fd40e26401757b99056a445c7bdca, dcc3b9d1dc2b99a16b70a9f8284aa82775f73fb6, f5e3f6d1b8b9ff81e12989eea1492cdaa0e35c00)

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 83.37%. Comparing base (cdbafd3) to head (aa986e2). :warning: Report is 26 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8726      +/-   ##
==========================================
+ Coverage   83.25%   83.37%   +0.12%     
==========================================
  Files         419      418       -1     
  Lines       32427    32488      +61     
==========================================
+ Hits        26997    27087      +90     
+ Misses       4047     4017      -30     
- Partials     1383     1384       +1     

Files with missing lines	Coverage Δ
credentials/tls.go	91.53% <100.00%> (+2.56%)	:arrow_up:

... and 58 files with indirect coverage changes

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[github-actions[bot]]

This PR is labeled as requiring an update from the reporter, and no update has been received after 6 days. If no update is provided in the next 7 days, this issue will be automatically closed.