HADOOP-18304. Improve user-facing S3A committers documentation (#4478)

[dannycjones]

Description of PR

Note: This is the same as #4478 but against branch-3.3.

As noted in the ticket, this PR attempts to improve the committer docs given a fresh pair of eyes from someone who has not worked with the committers before.

I've tried to ensure that the Table of Contents makes more sense too.

How was this patch tested?

No extra testing on top of existing tests in #4478.

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[dannycjones]

@mehakmeet backport of #4478

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 57s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+0 🆗	markdownlint	0m 0s		markdownlint was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
			_ branch-3.3 Compile Tests _
+1 💚	mvninstall	36m 42s		branch-3.3 passed
+1 💚	mvnsite	0m 59s		branch-3.3 passed
+1 💚	shadedclient	61m 20s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 41s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	mvnsite	0m 38s		the patch passed
+1 💚	shadedclient	23m 27s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	asflicense	0m 44s		The patch does not generate ASF License warnings.
		89m 11s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-5043/1/artifact/out/Dockerfile
GITHUB PR	#5043
Optional Tests	dupname asflicense mvnsite codespell detsecrets markdownlint
uname	Linux b799c366a72b 4.15.0-191-generic #202-Ubuntu SMP Thu Aug 4 01:49:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	branch-3.3 / 1e49149
Max. process+thread count	695 (vs. ulimit of 5500)
modules	C: hadoop-tools/hadoop-aws U: hadoop-tools/hadoop-aws
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-5043/1/console
versions	git=2.17.1 maven=3.6.0
Powered by	Apache Yetus 0.14.0 https://yetus.apache.org

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[hotcodemacha]

+1 LGTM

[steveloughran]

+1; merged. will cherrypick to 3.3.5 too

[dannycjones]

Thank you both!

[steveloughran]

doc updates always a welcome contribution