Add CredentialsProvider field to UniversalOptions

[dcherubini]

In #2097 go-redis started to support passing a CredentialsProvider callback to get the username and password when initializing a connection, instead of having to provide them when creating the client. This is very useful in scenarios where you have these credentials stored in a separate service (e.g., AWS Secret Manager or Azure Key Vault) and you want to rotate those credentials periodically.

However, this option was not added in all clients and was not being passed down from the universal client to the concrete clients either. This PR aims to normalize that.

(Note that the CredentialsProviders field was already added to ClusterOptions in #2791, which is why they are not being touched in this change)

[ndyakov]

Hello @dcherubini, We are introducing a new StreamingCredentialsProvider in #3320 and currently there is the CredentialsProviderContext (it's not a great name, I know). Would you mind updating the options in such a way to address those two as well? I was planing to do it myself, but wanted to keep you contribution and work with you on this PR instead of opening a new one.

[ndyakov]

@dcherubini the StreamingCredentialsProvider is added. Would you like to update this PR to add all credentials providers:

go-redis/options.go

Lines 68 to 84 in 86d418f

	// CredentialsProvider allows the username and password to be updated
	// before reconnecting. It should return the current username and password.
	CredentialsProvider func() (username string, password string)
	// CredentialsProviderContext is an enhanced parameter of CredentialsProvider,
	// done to maintain API compatibility. In the future,
	// there might be a merge between CredentialsProviderContext and CredentialsProvider.
	// There will be a conflict between them; if CredentialsProviderContext exists, we will ignore CredentialsProvider.
	CredentialsProviderContext func(ctx context.Context) (username string, password string, err error)
	// StreamingCredentialsProvider is used to retrieve the credentials
	// for the connection from an external source. Those credentials may change
	// during the connection lifetime. This is useful for managed identity
	// scenarios where the credentials are retrieved from an external source.
	//
	// Currently, this is a placeholder for the future implementation.
	StreamingCredentialsProvider auth.StreamingCredentialsProvider