pool: add Instance info to ConnectionInfo

[KaymeKaydex]

The Instance info has been added to ConnectionInfo, which is necessary to monitor the current state of the pool. This should help implement dynamic tracking of tarantool topology changes.

What has been done? Why? What problem is being solved?

I didn't forget about (remove if it is not applicable):

• Tests (see documentation for a testing package)
• Changelog (see documentation for changelog format)
• Documentation (see documentation for documentation style guide)

Related issues:

[themilchenko]

Thank you for the patch! Left a couple of minor comments below.

[themilchenko]

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Reference: https://www.tarantool.io/en/doc/latest/contributing/developer_guidelines/

[KaymeKaydex]

https://www.youtube.com/watch?v=KgIXSi-3JbY

[DerekBum]

Suggested change

	tCases = append(tCases, makeInstances([]string{
	servers[0],
	servers[1],
	servers[3]},
	connOpts))
	tCases = append(tCases, makeInstances([]string{
	servers[0],
	servers[1],
	servers[3],
	}, connOpts))

Nit, up to you.