Support certificates rotation

[ihab-soliman-form3]

Cockroachdb supports certificate rotation using sighup, visus does support sighup but it doesn't update the certificates used, the goal of this PR is to handle certificate rotation to be able to run visus as a sidecar with cockroachdb and both having the same process for certificate rotation.

Changes:

• Added a new switch flag when starting the server to enable reloading certificates, and defaulted to false for backward compatibility.

• Introduced two new exposed functions to the database factory instead of changing the original functions signature for both ease of use and not breaking a lot of places in the codebase. The reload function will be triggered (if enabled) on every new connection;

  Depending on the lifetime of the connection, when it ends, creating a new connection will always reload the certificates from the path.

  The Reset function on sighup will close all the connections but not close the pool, allowing new connections to be established.

Closes https://github.com/cockroachlabs/visus/issues/94

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This change is 

[sravotto]

Hi @ihab-soliman-form3, could you review and sign the Contributor License Agreement at https://cla.crdb.dev/cockroachlabs/visus ?

Thank you!

[sravotto]

@ihab-soliman-form3 thanks for the submission. However, in absence of a CLA we will be using #107 to implement the change requested.

Closing in favor of #107.

[ihab-soliman-form3]

@sravotto thank you