support `Strict-Transport-Security`, `Content-Security-Policy` and `X-Frame-Options`
HTTP headers in all VictoriaMetrics components.
The values for headers can be specified by users via the following flags:
`-http.header.hsts`, `-http.header.csp` and `-http.header.frameOptions`.
Co-authored-by: hagen1778 <roman@victoriametrics.com>
(cherry picked from commit ad839aa492)
Signed-off-by: hagen1778 <roman@victoriametrics.com>