[stable-2] mysql_replication: add deprecation warning about future replacement of Is_Slave and Is_Master return values, add alternatives (#147)

[Andersson007]

(cherry picked from commit 853db5a)

SUMMARY

Backport of #147

[codecov]

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[Andersson007]

cc @Jorge-Rodriguez @bmalynovytch
No need to review, just an example of the first backport to stable-2 which we should do for our and others' PRs we merge (except breaking changes, they will stay in main only).

There can be also cases, when a somebody else's PR contains both breaking and not breaking changes. In this case it would be
better to ask authors to split such PRs, otherwise we will have to extract non-breaking changes manually and backport which is not good:)

I'll write a short backport_guide.rst

If any questions, feel free to ask.

[Andersson007]

and yesterday i forgot to create stable-1 - created now. We should backport only bugfixes to stable-1.

I will try to use the backport bot to simplify the process.