Add cli option --tls-version to control tls version used

[meldafert]

Description

Fixes #1053.

This PR adds a --tls-version option, parallel to the option of the vanilla mysql client.
It was implemented by bypassing PyMySQL's ssl logic and creating the SSLContext ourselves.

This PR is currently a draft, as it would require raising the minimum python version to 3.7, as 3.6 has no way to force TLSv1.3.
Specifically, SSLContext.minimum_version was only added in 3.7.
However, PyMySQL's next update will require 3.7 as well.

This could alternatively be partially implemented inside PyMySQL as well. However, it is a documented option to pass a SSLContext to PyMySQL directly, so this seemed like the easier option.
One downside is that the _create_ssl_context method was strongly influenced by the one in PyMySQL - does this need to be noted somewhere for copyright reasons?

Checklist

• I've added this contribution to the changelog.md.
• I've added my name to the AUTHORS file (or it's already there).

[amjith]

I like the feature. I don't personally use ssl context so pardon my questions if they're too basic. I've left some questions inline for own clarification.

[codecov-commenter]

Codecov Report

Merging #1073 (1561834) into main (48bd4c9) will decrease coverage by 0.81%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##             main    #1073      +/-   ##
==========================================
- Coverage   67.92%   67.10%   -0.82%     
==========================================
  Files          26       26              
  Lines        2756     2791      +35     
==========================================
+ Hits         1872     1873       +1     
- Misses        884      918      +34     

Impacted Files	Coverage Δ
mycli/sqlexecute.py	74.40% <9.37%> (-9.55%)	⬇️
mycli/packages/completion_engine.py	61.90% <50.00%> (-0.17%)	⬇️
mycli/main.py	65.32% <100.00%> (+0.04%)	⬆️
mycli/sqlcompleter.py	82.53% <0.00%> (-1.75%)	⬇️

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[dveeden]

Might be good to consider lists/ranges of TLS versions.

• --tls-version TLSv1.2,TLSv1.3 Allowing these two versions only
• --min-tls-version TLSv1.2 Allowing TLSv1.2 and up

Might be good to by default only allow TLSv1.2 and up. See RFC 8996

[meldafert]

Thanks!