feat: added well-known did config enpoint to demo issuer

[birtony]

Signed-off-by: Anton Biriukov anton.biriukov@gendigital.com

[codecov[bot]]

Codecov Report

Patch coverage: 72.88% and project coverage change: -0.11 :warning:

Comparison is base (119908b) 79.03% compared to head (2bcf43e) 78.93%.

:exclamation: Current head 2bcf43e differs from pull request most recent head cd059a0. Consider uploading reports for the commit cd059a0 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1674 +/- ## ========================================== - Coverage 79.03% 78.93% -0.11% ========================================== Files 22 22 Lines 4546 4599 +53 ========================================== + Hits 3593 3630 +37 - Misses 678 686 +8 - Partials 275 283 +8 ``` | [Impacted Files](https://app.codecov.io/gh/trustbloc/sandbox/pull/1674?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trustbloc) | Coverage Δ | | |---|---|---| | [cmd/issuer-rest/startcmd/start.go](https://app.codecov.io/gh/trustbloc/sandbox/pull/1674?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trustbloc#diff-Y21kL2lzc3Vlci1yZXN0L3N0YXJ0Y21kL3N0YXJ0Lmdv) | `78.10% <66.66%> (-0.17%)` | :arrow_down: | | [pkg/restapi/issuer/operation/operations.go](https://app.codecov.io/gh/trustbloc/sandbox/pull/1674?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trustbloc#diff-cGtnL3Jlc3RhcGkvaXNzdWVyL29wZXJhdGlvbi9vcGVyYXRpb25zLmdv) | `77.87% <71.42%> (-0.24%)` | :arrow_down: | | [pkg/restapi/rp/operation/operations.go](https://app.codecov.io/gh/trustbloc/sandbox/pull/1674?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=trustbloc#diff-cGtnL3Jlc3RhcGkvcnAvb3BlcmF0aW9uL29wZXJhdGlvbnMuZ28=) | `71.65% <100.00%> (ø)` | |

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