*: fix more typos

[NathanBaulch]

Another batch of typos similar to #7487, plus a few minor grammar corrections.

FWIW, top 10 corrections are:

• existant -> existent (29)
• an -> a (13)
• a -> an (12)
• it's -> its (10)
• verificaiton -> verification (4)
• github -> GitHub (3)
• not -> no (2)
• certifcate -> certificate (2)
• unerlying underlying (1)
• panc -> panic (1)

RELEASE NOTES: none

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.02%. Comparing base (8f920c6) to head (bd1d023).
Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7619   +/-   ##
=======================================
  Coverage   82.01%   82.02%           
=======================================
  Files         361      361           
  Lines       27813    27890   +77     
=======================================
+ Hits        22812    22877   +65     
- Misses       3822     3826    +4     
- Partials     1179     1187    +8     

Files with missing lines	Coverage Δ
balancer/balancer.go	95.45% <ø> (ø)
balancer/base/balancer.go	85.18% <ø> (-2.78%)	⬇️
balancer/endpointsharding/endpointsharding.go	66.92% <ø> (ø)
balancer/grpclb/grpclb.go	82.67% <ø> (ø)
balancer/rls/internal/keys/builder.go	98.29% <ø> (ø)
clientconn.go	93.33% <ø> (+0.24%)	⬆️
dialoptions.go	89.02% <ø> (ø)
internal/grpcsync/callback_serializer.go	100.00% <ø> (ø)
internal/grpcutil/method.go	100.00% <ø> (ø)
internal/idle/idle.go	89.15% <ø> (ø)
... and 10 more

... and 16 files with indirect coverage changes

[purnesh42H]

thanks @NathanBaulch. Could you add the release notes?

[purnesh42H]

LGTM. Adding @arvindbr8 for second review

[arvindbr8]

Thanks for this. Looks like a very detailed review of our documentation.

[arvindbr8]

I can't seem to get Mergeable to run again. Trying a re-trigger by closing and reopening this PR