roll back go for notary binary

Fixes #14932

Harbor recompiles the notary v0.6.1 with go 1.15 from v2.2.0, which introduces an break change that leads to notary key not found after migration.

[Root cause]
Notary v0.6.1 consumed an old version dvsekhvalnov/jose2, which is not compatible with go 1.15.

[References]
https://github.com/dvsekhvalnov/jose2go/issues/26
https://github.com/golang/go/issues/41089

[Resolve]
To resolve this issue, we have to roll back go vesrion to v1.14 for notary v0.6.1 binary and keep it until upstream have a patch release to support go 1.15 or above.

[Break change]
If you pushed and signed image using Harbor v2.2.0 ~ v2.2.2 and created new repository key in notary, you will encouter the same issue after migrate to v2.2.3(or above) or v2.3.1(or above) because of the go version downgrade. We will have a FAQ to help you to resovle this particular scenario.

The influence path of the particular case:
Harbor v2.1.0(or lower) --> [v2.2.0 ~ v2.2.2] --> v2.2.3(or above)
Harbor v2.1.0(or lower) --> v2.3.0 --> v2.3.1(or above)

The non influence path of the paticular case:
Harbor v2.1.0(or lower) --> v2.2.3(or above)
Harbor v2.1.0(or lower) --> v2.3.1(or above)

[Fix in Version]
Harbor v2.2.3 or above
Harbor v2.3.1 or above

[Note]
If you're a heavy user of notary, avoid using v2.2.0, v2.2.1, v2.2.2 and v2.3.0, and use the fixed version for instead.

Signed-off-by: Wang Yan <wangyan@vmware.com>

make/photon/notary/binary.Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.15.12
+FROM golang:1.14.15
 
 ARG NOTARY_VERSION
 ARG MIGRATE_VERSION