MIM-2768 Migrate the docs to Zensical

[mdbrnowski]

This PR replaces Material for MkDocs with Zensical.

I also fixed a few broken links and anchors, and rewrote PlantUML diagrams to Mermaid.

[mongoose-im]

CircleCI results for ab9ae5a

---

small_tests_latest / small_tests / 4918350
Reports root / small

---

small_tests_legacy / small_tests / 4918350
Reports root / small

---

small_tests_latest_arm64 / small_tests / 4918350
Reports root / small

---

internal_mnesia_latest / internal_mnesia / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 2444 / Failed: 0 / User-skipped: 1416 / Auto-skipped: 0

---

ldap_mnesia_latest / ldap_mnesia / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 2295 / Failed: 0 / User-skipped: 1565 / Auto-skipped: 0

---

dynamic_domains_pgsql_cets_legacy / pgsql_cets / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5154 / Failed: 0 / User-skipped: 237 / Auto-skipped: 0

---

dynamic_domains_pgsql_cets_latest / pgsql_cets / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5154 / Failed: 0 / User-skipped: 237 / Auto-skipped: 0

---

elasticsearch_and_cassandra_mnesia_latest / elasticsearch_and_cassandra_mnesia / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 3111 / Failed: 0 / User-skipped: 1444 / Auto-skipped: 0

mongoose_elasticsearch_SUITE:end_per_suite

{error,
  {{badrpc,
     {'EXIT',
       {#{what => event_already_registered,
        event_name => wpool_global_queue_lengths,
        labels => #{pool_tag => default,pool_type => elastic}},
        [{mongoose_instrument,set_up,3,
           [{file,
            "/home/circleci/project/src/instrument/mongoose_instrument.erl"},
          {line,114}]},
         {lists,foreach_1,2,[{file,"lists.erl"},{line,2641}]},
         {mongoose_wpool,start,5,
           [{file,
            "/home/circleci/project/src/wpool/mongoose_wpool.erl"},
          {line,162}]},
         {mongoose_wpool,'-start_configured_pools/3-lc$^1/1-1-',1,
           [{file,
            "/home/circleci/project/src/wpool/mongoose_wpool.erl"},
          {line,129}]},
         {mongoose_wpool,start_configured_pools,1,[]}]}}},
   [{distributed_helper,rpc,
      [#{node => mongooseim@localhost},
       mongoose_wpool,start_configured_pools,
       [[#{scope => global,tag => default,type => elastic,
         opts =>
           #{strategy => best_worker,workers => 10,
           call_timeout => 5000},
         conn_opts => #{port => 9200,host => <<"localhost">>}}]]],
      [{file,
         "/home/circleci/project/big_tests/../test/common/distributed_helper.erl"},
       {line,143}]},
    {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1799}]},
    {test_server,run_test_case_eval1,6,
      [{file,"test_server.erl"},{line,1396}]},
    {test_server,run_test_case_eval,9,
      [{file,"test_server.erl"},{line,1240}]}]}...

Report log

---

pgsql_cets_legacy / pgsql_cets / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5475 / Failed: 0 / User-skipped: 213 / Auto-skipped: 0

---

pgsql_redis_latest / pgsql_redis / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5555 / Failed: 0 / User-skipped: 378 / Auto-skipped: 0

---

mysql_cets_latest / mysql_cets / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5473 / Failed: 0 / User-skipped: 215 / Auto-skipped: 0

---

pgsql_cets_latest / pgsql_cets / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5475 / Failed: 0 / User-skipped: 213 / Auto-skipped: 0

---

cockroachdb_cets_latest / cockroachdb_cets / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5475 / Failed: 0 / User-skipped: 213 / Auto-skipped: 0

---

pgsql_mnesia_latest / pgsql_mnesia / 4918350
Status: 🟢 Passed
Reports root/ big
OK: 5589 / Failed: 0 / User-skipped: 344 / Auto-skipped: 0

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.92%. Comparing base (00696e3) to head (4918350).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4763   +/-   ##
=======================================
  Coverage   86.92%   86.92%           
=======================================
  Files         552      552           
  Lines       33369    33369           
=======================================
+ Hits        29005    29006    +1     
+ Misses       4364     4363    -1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.