PyMySQL: Improve Connection __init__ overloads & add missing types

[el1s7]

• Replace Incomplete with more accurate types where possible
• Add missing ssl_key_password parameter to the second __init__ overload

And some other small improvements.

[brianschubert]

Thanks! LG, left a few suggestions below

[el1s7]

Thanks @brianschubert , I didn't look carefully at all the attributes before, I have added all your suggestions.

Additionally, I added two overloads for deprecating passwd and db.

And I put the SSL configuration options in a TypedDict for re-using them with Unpack, just for reducing the amount of repetitive arguments in the overloads.

Let me know if any additional changes are needed.

Edit: I wasn't aware that Unpack arguments are not supported in stub files, I have included all arguments explicitly in the overloads. My bad, I should've run the stub tests locally first before commiting 😅

[brianschubert]

Thanks! Two last remarks about comments

[brianschubert]

Looks good, thank you! One final request about some removed attributes, then this is good to go

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

discord.py (https://github.com/Rapptz/discord.py)
- discord/ext/commands/hybrid.py:834: error: Overlap between argument names and ** TypedDict items: "with_app_command", "name"  [misc]
+ discord/ext/commands/hybrid.py:834: error: Overlap between argument names and ** TypedDict items: "name", "with_app_command"  [misc]
- discord/ext/commands/hybrid.py:858: error: Overlap between argument names and ** TypedDict items: "with_app_command", "name"  [misc]
+ discord/ext/commands/hybrid.py:858: error: Overlap between argument names and ** TypedDict items: "name", "with_app_command"  [misc]
- discord/ext/commands/hybrid.py:883: error: Overlap between argument names and ** TypedDict items: "with_app_command", "name"  [misc]
+ discord/ext/commands/hybrid.py:883: error: Overlap between argument names and ** TypedDict items: "name", "with_app_command"  [misc]
- discord/ext/commands/hybrid.py:935: error: Overlap between argument names and ** TypedDict items: "with_app_command", "name"  [misc]
+ discord/ext/commands/hybrid.py:935: error: Overlap between argument names and ** TypedDict items: "name", "with_app_command"  [misc]
- discord/ext/commands/bot.py:290: error: Overlap between argument names and ** TypedDict items: "with_app_command", "name"  [misc]
+ discord/ext/commands/bot.py:290: error: Overlap between argument names and ** TypedDict items: "name", "with_app_command"  [misc]
- discord/ext/commands/bot.py:314: error: Overlap between argument names and ** TypedDict items: "with_app_command", "name"  [misc]
+ discord/ext/commands/bot.py:314: error: Overlap between argument names and ** TypedDict items: "name", "with_app_command"  [misc]