Fix Go routine leaks in streaming calls

[GuptaManan100]

Description

This PR fixes the issue described in #14201.

On following the steps listed in the issue, it was noticed that we indeed had a bunch of go-routines being spawned off, that never really went away -

goroutine profile: total 102
31 @ 0x102aaf7e8 0x102ac2c38 0x103033f0c 0x102ae9dc4
#	0x103033f0b	google.golang.org/grpc.newClientStreamWithParams.func4+0x8b	google.golang.org/[email protected]/stream.go:393

Notice the count of the go-routines which are all on the same line. Its 31, but running the queries in a loop causes it to increase by 1 for each iteration.

The problem causes go-routines to leak which will eventually lead to an OOM. The fix however was pretty straightforward.
In the StreamExecute RPC code, we have the following comment

vitess/go/vt/vttablet/grpctabletconn/conn.go

Lines 142 to 151 in f1a95e1

	// All streaming clients should follow the code pattern below.
	// The first part of the function starts the stream while holding
	// a lock on conn.mu. The second part receives the data and calls
	// callback.
	// A new cancelable context is needed because there's currently
	// no direct API to end a stream from the client side. If callback
	// returns an error, we return from the function. The deferred
	// cancel will then cause the stream to be terminated.
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

This however wasn't being followed in the other streaming RPCs, like BeginStreamExecute causing the go routines to leak.

Related Issue(s)

• Fixes Bug Report: Potential leak of non-stopping goroutines #14201

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (696fe0e) 67.41% compared to head (316de39) 67.54%.
Report is 34 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15293      +/-   ##
==========================================
+ Coverage   67.41%   67.54%   +0.12%     
==========================================
  Files        1560     1561       +1     
  Lines      192752   193371     +619     
==========================================
+ Hits       129952   130613     +661     
+ Misses      62800    62758      -42     

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[GuptaManan100]

Leaking go routines is a serious issue, and therefore the fix is being backported.

[harshit-gangal]

There are other methods as well
VStream, VStreamRows, VStreamTables, VStreamResults and GetSchema which should also have the same cancelable code block

[GuptaManan100]

@harshit-gangal Super catch! I've fixed them too 💯