Reference doc bug bash (look for both content issues and rendering issues) for Key Vault

[AlexGhiondea]

[lmazuel]

Duplicate of #15121

[mccoyp]

Below are the rendering issues found in the reference docs -- some are rendering/linking related, while some are content-related but need further investigation before fixing in source code.

Bug type	Description	Source
Docs content	General KV overview page mentions that 4.x is recommended under "Libraries for data access", but there should also be a note about this under "Version 1.x.x"	link
Rendering	Management library overview page is empty on docs, despite there being non-empty (even if sparse) READMEs on GitHub. We'll need to follow up with Scott to see why this is	link
Linking	Clicking the "Reference" link for azure-keyvault from KV overview page brings up the preview KV overview instead of the legacy overview	link
Docs content	README that's linked to from the azure-keyvault "GitHub" link in reference docs is in a tag (but not a branch) in the repo. The link to the reference docs from the README is outdated, but I'm not sure how to update it to the legacy docs page since there's no branch with the legacy README content	link
Linking	Link for Python in the "Reference" TOC node in the KV service overview page directs to the management package reference, when it should probably link to the general KV overview	link
Content/rendering	begin_create_certificate shows "HttpResponseError" under "Exceptions" twice, and lists all possible parameters as "Required" when some are optional keyword-only arguments. These issues exist for all methods that have required parameters (denoted by :param x x: in their docstring) as well as keyword arguments specified in their docstring (denoted by :keyword x x:). Methods that have only keyword arguments denoted by :keyword x x: don't render with duplicate exceptions in the reference docs, but their parameters are still listed as "Required". Keyword arguments that are denoted by :param x x: in docstrings don't show up as "Required" (see JsonWebKey), but these can't coexist with required parameters	link
Content/rendering	KeyVaultKey has code block examples in its docstring, such that they render in the package class list and aren't put in an "Examples" section like we do for other classes. Should this be changed? Can multiple examples be put in a single docstring using the Example: literalinclude:: pattern?	link