Allow records to be annotated with @http:Header

[shafreenAnfar]

This is related to Proposal [1]. Instead of doing the below,

resource function get hello(@http:Header string x\-rate\-limit\-id,  @http:Header int x\-rate\-limit\-remaining, @http:Header string[] x\-rate\-limit\-types) returns string {
}

Users should be able to do the below,

public type RateLimitHeaders record {|
    string x\-rate\-limit\-id;
    int x\-rate\-limit\-remaining;
    string[] x\-rate\-limit\-types;
|};

resource function get hello(@http:Headers RateLimitHeaders rateLimitHeaders) returns string {
}

[1] https://github.com/ballerina-platform/module-ballerina-http/blob/master/docs/proposals/typed-headers.md