Add support for search parameters

[paramsiddharth]

Add support for search parameters

For the GET requests made to the /api/certificate and /api/template routes, query parameters may be used to filter the results to be sent back.

Examples:

• GET /api/certificate?template=abcd should return all the certificates with the template of ID abcd.
• GET /api/template?tags=%5B%22a%22%2C%22bc%22%2C%22d%22%5D should return all the templates with tags a, bc, and d at the same time. %5B%22a%22%2C%22bc%22%2C%22d%22%5D is nothing but the encoded form of JSON.stringify(['a', 'bc', 'd']).

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