Signed-off-by: Miek Gieben <miek@miek.nl>

* Add SVCB dohpath key

The parameter is being added in [its own IETF draft][1] and also being used in
the [IETF draft about Descovery of Designated Resolvers][2].

Additionally, the mappings of the numeric key values to strings are exported,
under names consistent with the already existing exported mappings, to make it
easier for the clients of the module to validate and print SVCB keys.

Testing was done by sending SVCB queries for the "_dns.resolver.arpa" domain to
OpenDNS's 146.112.41.2 server.

[1]: https://datatracker.ietf.org/doc/html/draft-ietf-add-svcb-dns-02
[2]: https://datatracker.ietf.org/doc/html/draft-ietf-add-ddr-06.html

* Fix template length, docs; reverse some changes

* Remove incorrect validations; improve docs

* Add notes about SVCB draft changes to SVCB-related API

* Decrease number of warnings, rephrase

Small fix in the examples to properly work with v6 addresses.

Closes: #1365 #1367

Signed-off-by: Miek Gieben <miek@miek.nl>

Signed-off-by: Miek Gieben <miek@miek.nl>

* Modify the SVCBAlpn to properly parse/print

* Remove debug

* Change SVCB test from reflect to loop

* Refactor SVCB code to reduce indentation

* When stringifying SVCBAlpn, use strings.Builder for whole process

* Update comment in svcb.go

Co-authored-by: Miek Gieben <miek@miek.nl>

* Describe why we use a specific size for the alpn buffer

Co-authored-by: Miek Gieben <miek@miek.nl>

* dohpath escaped in String(), and parsed such values

* Update the test for dohpath with escaping

* Fix cut & paste error with svcdohpath error