Add initial support for configuration through MDM

[stefanceriu]

This will allow MDM providers to configure the:

• default homeserver URL - im.vector.app.serverConfigDefaultHomeserverUrlString
• push gateway URL - im.vector.app.serverConfigSygnalAPIUrlString
• permalink base URL - im.vector.app.clientPermalinkBaseUrl

These methods will always try to fetch the MDM configuration first, if available, otherwise they will just use the existing defaults.

[codecov[bot]]

Codecov Report

Patch coverage: 85.71% and project coverage change: +0.22% :tada:

Comparison is base (fef3077) 12.00% compared to head (d4c9a0a) 12.22%. Report is 4 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #7667 +/- ## =========================================== + Coverage 12.00% 12.22% +0.22% =========================================== Files 1648 1649 +1 Lines 163748 163777 +29 Branches 67202 67226 +24 =========================================== + Hits 19655 20019 +364 + Misses 143435 143111 -324 + Partials 658 647 -11 ``` | [Flag](https://app.codecov.io/gh/vector-im/element-ios/pull/7667/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | Coverage Δ | | |---|---|---| | [uitests](https://app.codecov.io/gh/vector-im/element-ios/pull/7667/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | `54.96% <0.00%> (-0.09%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/vector-im/element-ios/pull/7667/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | `6.07% <85.71%> (+0.22%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/vector-im/element-ios/pull/7667?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | Coverage Δ | | |---|---|---| | [Config/MDMSettings.swift](https://app.codecov.io/gh/vector-im/element-ios/pull/7667?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im#diff-Q29uZmlnL01ETVNldHRpbmdzLnN3aWZ0) | `78.94% <78.94%> (ø)` | | | [Config/BuildSettings.swift](https://app.codecov.io/gh/vector-im/element-ios/pull/7667?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im#diff-Q29uZmlnL0J1aWxkU2V0dGluZ3Muc3dpZnQ=) | `50.00% <100.00%> (+6.92%)` | :arrow_up: | ... and [27 files with indirect coverage changes](https://app.codecov.io/gh/vector-im/element-ios/pull/7667/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im)

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[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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