Allow services to include metadata links and metadata ETags into responses

Allow services to annotate the odata.metadata annotation with the odata.etag annotation to transport the current ETag of $metadata to clients: { "odata.metadata": "http://host/service/$metadata", "odata.metadata@odata.etag": "A1FF3E230954908F", ... } Allow services to return etag in metadata request and add a metadata link that MAY contain a metadata:etag attribute to Atom responses: <link rel="http://docs.oasis-open.org/odata/ns/metadata" metadata:etag="A1FF3E230954908F" href="http://host/service/$metadata" /> metadata is same as odata.metadata annotation in json. Accepted: https://www.oasis-open.org/committees/download.php/48752/odata-meeting-31_on-20130404-minutes.html#odata-319

https://tools.oasis-open.org/version-control/browse/wsvn/odata/trunk/spec/schemas/metadata.xsd?rev=239 https://www.oasis-open.org/apps/org/workgroup/odata/download.php/48905/odata-atom-format-v4.0-wd01-2013-4-23.docx https://www.oasis-open.org/apps/org/workgroup/odata/download.php/48902/odata-core-v4.0-wd01-part1-2013-4-23.docx https://www.oasis-open.org/apps/org/workgroup/odata/download.php/48904/odata-json-format-v4.0-wd01-2013-4-23.docx Accepted: https://www.oasis-open.org/committees/download.php/49026/odata-meeting-34_on-20130425_26-F2F-minutes.html#odata-319