Fix empty path in request-target

[anbraten]

If the path of the url is currently empty `` instead of / the signing fails.

From RFC7540 Section 8.1.2.3:

This pseudo-header field MUST NOT be empty for "http" or "https"
URIs; "http" or "https" URIs that do not contain a path component
MUST include a value of '/'. The exception to this rule is an
OPTIONS request for an "http" or "https" URI that does not include
a path component; these MUST include a ":path" pseudo-header field
with a value of '*' (see [RFC7230], Section 5.3.4).

In addition I have added the (request-target) data to the actual headers when requested by the user.

[6543]

@cjslep is this lib still maintained ?

ref: woodpecker-ci/example-config-service#10