[OCM] Make webdav URL absolute according to spec

[VicDeo]

Description

Return an absolute URL for OCM WebDav discovery endpoint and change the storage to work with absolute discovery URLs

Note: It makes OCM-based sharing in 10.1 incompatible with 10.2+ without patching apps/files_sharing/lib/External/Storage.php

Related Issue

• Fixes OCM Returned endpoint relative #34631

Motivation and Context

To comply with OCM 1.0.0-proposal1 spec

How Has This Been Tested?

open URL owncloud.tld/ocm-provider/

expected

{"enabled":true,"apiVersion":"1.0-proposal1",
"endPoint":"http:\/\/owncloud.tld\/index.php\/apps\/federatedfilesharing",
"shareTypes":[{"name":"file",
"protocols":{"webdav":"http:\/\/owncloud.tld\/public.php\/webdav\/"}}]}

actual

{"enabled":true,"apiVersion":"1.0-proposal1",
"endPoint":"http:\/\/owncloud.tld\/index.php\/apps\/federatedfilesharing",
"shareTypes":[{"name":"file",
"protocols":{"webdav":"\/public.php\/webdav\/"}}]}

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

Open tasks:

• Backport (if applicable set "backport-request" label and remove when the backport was done)

[codecov]

Codecov Report

Merging #34260 into master will decrease coverage by <.01%.
The diff coverage is 41.66%.

@@             Coverage Diff              @@
##             master   #34260      +/-   ##
============================================
- Coverage     65.25%   65.25%   -0.01%     
- Complexity    18457    18459       +2     
============================================
  Files          1207     1207              
  Lines         69887    69897      +10     
  Branches       1280     1280              
============================================
+ Hits          45608    45611       +3     
- Misses        23907    23914       +7     
  Partials        372      372

Flag	Coverage Δ	Complexity Δ
#javascript	53.04% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	66.65% <41.66%> (-0.01%)	18459 <0> (+2)

Impacted Files	Coverage Δ	Complexity Δ
...eratedfilesharing/lib/Controller/OcmController.php	66.26% <100%> (ø)	30 <0> (ø)	⬇️
apps/files_sharing/lib/External/Storage.php	28.67% <36.36%> (+0.09%)	51 <0> (+2)	⬆️

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[micbar]

Needs to be tested with federation behind a reverse proxy.

I will take care.

[DeepDiver1975]

As discussed in #35777 the master branch will from now on hold the ownCloud 10 codebase.

This PR targetted ownCloud 11 which is postponed to a far distant future.

Because of that I'm closing this PR and kindly ask you to re-submit this PR in a few days.

Thanks a lot for your patience

[VicDeo]

resubmitted as #36043