#1509 fetch() implementation

[rrrooommmaaa]

This PR replaces JQuery ajax calls with fetch()
Modifies the mock API to use HTTP/2 -- required to display fetch upload progress.

issue #1509

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Tests(delete all except exactly one):

• Does not need tests (refactor only, docs or internal changes)

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[sosnovsky]

@ioanmo226 this issue is part of bigger refactoring to implement Manifest V3 requirements, which should be required in the future for all extensions. In this PR we switch to using fetch instead of Jquery.Ajax, as in V3 it's not possible to use XMLHTTPRequest (which is used by Jquery.Ajax).

Roman worked on this switch, but there were some issues in loading messages in Firefox, as currently it doesn't support some features of fetch. So I worked on implementing fallbacks which use XMLHTTPRequest, but can be removed and switched to fetch when all needed functionality will be implemented there.

[sosnovsky]

By the way, might better to add another reviewer as this seems breaking changes and I might have missed something? Like @tomholub or @rrrooommmaaa ?

Unfortunately Roman doesn't work on FlowCrypt anymore, that's why I was finalising this PR.
Tom checked this PR before I started working on it, looked good for him. I worked mostly on fixing issues found during previous reviews, so I think it shouldn't break anything as currently all tests are passing without issues.

[sosnovsky]

Please check test

We've missed that Google API urls have different base urls - ${GMAIL_GOOGLE_API_HOST}/gmail/v1/users/me and ${GMAIL_GOOGLE_API_HOST}/upload/gmail/v1/users/me, so it caused test fails.
Reverted this change, tests should pass now