Backport "HBASE-24144 Update docs from master" to branch-2.3

[ndimiduk]

Bring back documentation from master branch (2ecbaf1), using

$ git checkout master -- src/main/asciidoc/
$ git checkout master -- src/site/asciidoc/

And then:

• remove changes from HBASE-23890
  This reverts commit 420e380.
• delete docs re: sync_replication
• delete docs re: backup

[Apache-HBase]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	0m 43s	Docker mode activated.
-0 ⚠️	yetus	0m 8s	Unprocessed flag(s): --brief-report-file --spotbugs-strict-precheck --whitespace-eol-ignore-list --whitespace-tabs-ignore-list --quick-hadoopcheck
		_ Prechecks _
		_ branch-2.3 Compile Tests _
		_ Patch Compile Tests _
		_ Other Tests _
		2m 13s

Subsystem	Report/Notes
Docker	Client=19.03.11 Server=19.03.11 base: https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/artifact/yetus-jdk8-hadoop2-check/output/Dockerfile
GITHUB PR	#1904
Optional Tests
uname	Linux 0895818b4668 4.15.0-60-generic #67-Ubuntu SMP Thu Aug 22 16:55:30 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
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git revision	branch-2.3 / fc1da63
Max. process+thread count	52 (vs. ulimit of 12500)
modules	C: . U: .
Console output	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/console
versions	git=2.17.1 maven=(cecedd343002696d0abb50b32b541b8a6ba2883f)
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[Apache-HBase]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	2m 30s	Docker mode activated.
-0 ⚠️	yetus	0m 6s	Unprocessed flag(s): --brief-report-file --spotbugs-strict-precheck --whitespace-eol-ignore-list --whitespace-tabs-ignore-list --quick-hadoopcheck
		_ Prechecks _
		_ branch-2.3 Compile Tests _
		_ Patch Compile Tests _
		_ Other Tests _
		3m 51s

Subsystem	Report/Notes
Docker	Client=19.03.11 Server=19.03.11 base: https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/artifact/yetus-jdk11-hadoop3-check/output/Dockerfile
GITHUB PR	#1904
Optional Tests
uname	Linux 19ddc12773ca 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/hbase-personality.sh
git revision	branch-2.3 / fc1da63
Max. process+thread count	50 (vs. ulimit of 12500)
modules	C: . U: .
Console output	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/console
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[Apache-HBase]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	1m 8s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 1s	No case conflicting files found.
+1 💚	@author	0m 0s	The patch does not contain any @author tags.
		_ branch-2.3 Compile Tests _
+1 💚	mvninstall	3m 52s	branch-2.3 passed
+1 💚	mvnsite	26m 8s	branch-2.3 passed
+0 🆗	refguide	7m 14s	branch has no errors when building the reference guide. See footer for rendered docs, which you should manually inspect.
		_ Patch Compile Tests _
+1 💚	mvninstall	3m 30s	the patch passed
+1 💚	mvnsite	21m 35s	the patch passed
-0 ⚠️	whitespace	0m 0s	The patch has 51 line(s) that end in whitespace. Use git apply --whitespace=fix <<patch_file>>. Refer https://git-scm.com/docs/git-apply
+0 🆗	refguide	7m 25s	patch has no errors when building the reference guide. See footer for rendered docs, which you should manually inspect.
		_ Other Tests _
+1 💚	asflicense	0m 12s	The patch does not generate ASF License warnings.
		72m 51s

Subsystem	Report/Notes
Docker	Client=19.03.11 Server=19.03.11 base: https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/artifact/yetus-general-check/output/Dockerfile
GITHUB PR	#1904
Optional Tests	dupname asflicense refguide mvnsite
uname	Linux 8de7128cad67 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/hbase-personality.sh
git revision	branch-2.3 / fc1da63
refguide	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/artifact/yetus-general-check/output/branch-site/book.html
whitespace	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/artifact/yetus-general-check/output/whitespace-eol.txt
refguide	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/artifact/yetus-general-check/output/patch-site/book.html
Max. process+thread count	84 (vs. ulimit of 12500)
modules	C: . U: .
Console output	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1904/1/console
versions	git=2.17.1 maven=(cecedd343002696d0abb50b32b541b8a6ba2883f)
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